Barry Trost

A new bifunctional ligand bearing chiral N‐heterocyclic carbene (NHC) and prolinol moieties is presented. Utilizing the designed ligand, an in situ formed Cu/Zn hetero‐bimetallic complex unlocks the asymmetric allylic alkylation reactions of allyl phosphates with zinc keto‐homoenolates, leading to the formation of various γ‐vinyl ketones with good regio‐ and enantio‐selectivity. DF sT calculation supports that the chelation of allyl phosphates with catalyst promotes the SN2’ addition and the ligand‐substrate steric interactions account for the stereoselective outcome.

A novel Pd0‐catalyzed highly regio‐ and enantioselective [3+2] spiroannulation reaction has been developed for rapid assembly of a new class of [5,5] spirocyclic carbo‐ and heterocycles. Notably, the regioselectivity could be dominated by fine‐tuning of the Pd‐π‐allyl intermediate. An array of coupling partners could be well‐tolerated with excellent regio‐, and enantioselectivities. Moreover, the potential application of this reaction was exemplified by several further transformations.

We synthesized a series of phosphine–olefin-type chiral aminophosphines, and we confirmed that these each exists as two rotamers at the C(aryl)–N(amine) bond. We also investigated the ability of these aminophosphines to act as chiral ligands for Pd-catalyzed asymmetric allylic substitution reactions, such as the alkylation of allylic acetates with malonates or indoles, and we found they gave high enantioselectivities (up to 98% ee).

The first total synthesis of the trimethyl ester of kadcoccinic acid A is described. The central structural element of our synthesis is a cyclopentenone motif that allows the assembly of the natural product skeleton. A gold(I)-catalyzed cyclization of an enynyl acetate led to efficient construction of the cyclopentenone scaffold. In this step, optimization studies revealed that the stereochemistry of the enynyl acetate dictates regioisomeric cyclopentenone formation. The synthesis further highlights an efficient copper-mediated conjugate addition, merged with a gold(I)-catalyzed Conia-ene reaction to connect the two fragments, thereby forging the D-ring of the natural product. The synthetic strategy reported herein can provide a general platform to access the skeleton of other members of this family of natural products.

A method for the Brønsted acid promoted desulfination of aryl sulfoxides is presented. In the presence of a thiol, electron-rich sulfoxides undergo C–S bond cleavage to give the corresponding protodesulfinated arenes and disulfides.

The synthesis of the pentacylic core of (+)-citrinadin A is described. Our strategy harnesses the power of palladium-catalyzed trimethylenemethane chemistry (Pd-TMM) to form the key spirooxindole motif in a catalytic, asymmetric fashion. Upon the conversion of this spirooxindole to a vinyl epoxide electrophile, the piperidine ring is directly added via a diastereoselective metalation followed by an SN2′ addition. The final ring of the pentacyclic core is then formed through an intramolecular SN2 displacement of the resulting activated alcohol.

A highly regio-, diastereo-, and enantioselective trimethylenemethane (TMM) cycloaddition reaction for the rapid assembly of 2-acyl-methylenecyclopentane in an atom-economic fashion is described. This intermolecular protocol allows for facile and divergent access to an array of structurally attractive cyclic adducts. The choice of a robust chiral diamidophosphite ligand, developed by our group, proved to be crucial for the success of this transformation.

The palladium-catalyzed [3 + 2] cycloaddition using in situ generated sulfone-TMM species to construct various chiral cyclopentyl sulfones in a highly regio-, diastereo- (dr >15:1), and enantioselective (up to 99% ee) manner is reported. The present strategy can tolerate different types of sulfone-TMM donors and acceptors, and enables the construction of three chiral centers in a single step, specifically with a chiral center bearing the sulfone moiety. The robust chiral diamidophosphite ligand is the key to the reactivity and selectivities of this transformation.

An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pKa limitation of “hard” nucleophiles in enantioselective transformations.

We report the preparation of phosphiranium salts by quaternarization of phosphiranes, a class of sensitive, highly strained, and poorly nucleophilic cyclic phosphines. High-yielding introduction of a varied set of alkyl groups including methylene ester arms was accomplished under mild conditions. A Cu-catalyzed electrophilic arylation of phosphiranes using diaryl iodonium reagents was also achieved to yield unprecedented P,P-diaryl phosphiranium salts with good efficiency.

ProPhenol‐Moleküle gehören zur Gruppe der chiralen Azakronen‐Verbindungen und bilden bei Umsetzung mit Alkylmetall‐Reagenzien wie Et2Zn und Bu2Mg spontan einen bimetallischen Komplex. Dieser Komplex hat Lewis‐saure und Brønsted‐basische Reaktionszentren, die eine simultane Aktivierung eines Nukleophils und eines Elektrophils in derselben chiralen Umgebung erlauben. Seit dem ersten Bericht im Jahr 2000 haben Metall‐ProPhenol‐Katalysatoren eine große Bandbreite asymmetrischer Umwandlungen wie Aldol‐, Mannich‐ und Henry‐Reaktionen sowie Alkinylierungen und konjugierte Additionen ermöglicht. Aufgrund der vielfältigen Einsatzmöglichkeiten bei unterschiedlichen Reaktionen erlauben diese Komplexe einen schnellen und atomökonomischen Zugang zu wertvollen komplexen Baugruppen. In diesem Aufsatz beschreiben wir detailliert die Entwicklung und synthetischen …

ConspectusThe catalytic asymmetric synthesis of complex molecules has been the focus of our research program for several decades because such strategies have significant utility for the construction of chiral building blocks for drug development as well as the total synthesis of natural products. Cycloaddition reactions are very powerful transformations in organic synthesis providing access to highly functionalized motifs from simple starting materials. In concert with this central interest, four decades ago, we reported the palladium-catalyzed trimethylenemethane (TMM) cycloaddition for forging odd-membered ring systems. In recent years, we focused our attention on the development of powerful ligand scaffolds which enable the preparation of valuable products with complete control of chemo-, regio-, diastereo-, and enantioselectivity, thereby addressing several limitations in the field of palladium-catalyzed …

The palladium-catalyzed unified approach using in situ-generated Phospha-TMM species to synthesize a diverse array of chiral organophosphorus containing carbo- and heterocyclic compounds in a highly regio-, diastereo- (>20:1 dr), and enantioselective (>99% ee) fashion is being disclosed. The present protocol reveals the potential of the deprotonative phospha-TMM strategy for the synthesis of challenging five-membered carbo- and heterocycles, especially those with spirocyclic entities and quaternary asymmetric stereocenters. The choice of the robust chiral diamidophosphite ligand proved to be very crucial for the desired reactivity in the present transformation. Furthermore, the synthetic utility of the products is demonstrated by multiple transformations such as reductions, oxidations, and alkylations.

Organophosphorus pyrrolidine derivatives possessing P–N bonds are a promising yet underexplored class of compounds. In this short review we overview the general approaches to these compounds described so far, with a special emphasis on their asymmetric synthesis. 1 Introduction 2 Synthesis of Pyrrolidine-Based P(III) Derivatives 3 Synthesis of Pyrrolidine-Based P(V) Derivatives 3.1 Phosphorylation of Pyrrolidines with P(V) Acid Chlorides 3.2 Phosphorylation of Pyrrolidines with P(V) Acid Esters 3.3 Syntheses via the Atherton–Todd Reaction 3.4 Oxidation of Pyrrolidine-Based P(III) Derivatives 4 Syntheses of N-Phosphorylpyrrolidines from Acyclic Precursors 5 Conclusions

A palladium-catalyzed oxidative C–H allylic alkylation of N-hydroxyimides has been developed. This transformation provided valuable N-allyloxypyrrolidinediones in moderate to excellent yields using operationally simple, ligand free, and mild reaction conditions. The reaction tolerated broad and variable substituents on allylarenes and N-hydroxyimides.

Herein, we described a ligand-free copper-catalyzed aerobic oxidative functionalization of 3,4-dihydroquinoxalin-2(1H)-ones with terminal alkynes using visible-light and oxygen as terminal oxidant to give 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-one, cyclic propargylic amines, in moderate to good yields. Moreover, we demonstrate the versatility of the 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-ones obtained by preparing several 3,4-dihydroquinoxalin-2-one derivatives.

In the reactions of simple starting materials, precise catalytic control of the stereochemical outcome (enantio- and diastereoselectivity), as well as chemoselectivity and regioselectivity is an efficient approach to increase molecular complexity with minimal use of protecting groups. Here, we introduce our ongoing studies on asymmetric catalytic reactions using α-keto esters as pronucleophiles or formal 1,3-dipolarophiles. Capitalizing on the high tunability of our late transition-metal complexes with a suitable basic counteranion, we have established a range of multiselective catalytic protocols starting from α-keto esters to provide a wide variety of stereochemically complex molecules incorporating adjacent stereocenters. 1 Introduction 2 Catalytic Asymmetric Monofluorination with NSFI 3 Catalytic Asymmetric Michael Reaction with Nitroolefins 4 Catalytic Asymmetric [3+2] Cycloaddition with (E)-Nitrones 5 Catalytic …

The 3a-hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic acid (HPIC) residue and its aza-analogue are found in many bioactive natural products. In this account, short divergent total syntheses of several such natural products, diastereomers and analogues are described. It is demonstrated that by appropriate combination of different efficient tactics such as biomimetic/bio-inspired synthesis, chemo/regioselective reactions, umpolung of regioselectivity and/or reactivity, and tandem reactions, the enantioselective syntheses of polycyclic molecules such as (+)-asperlicin E and (–)-robustanoids A and B can be achieved in a protecting-group-free and redox-economical manner, in only three to four steps starting from l-tryptophan. 1 Introduction 2 Strategic Considerations 2.1 Occurrence of HO-HPIC and HO-aza-HPIC Residues in Natural Products 2.2 Biosyntheses of HO-HPIC and HO-aza-HPIC Residues 2.3 …

Five-carbon dimethylallyl units, such as prenyl and reverse-prenyl, are widely distributed in natural indole alkaloids and terpenoids. In conventional methodologies, these valuable motifs are often derived from substrates bearing leaving groups, but these processes are accompanied by the generation of stoichiometric amounts of by-products. From an economical and environmental point of view, the basic industrial feedstock isoprene is an ideal alternative precursor. However, given that electronically unbiased isoprene might undergo six possible addition modes in the coupling reactions, it is difficult to control the selectivity. This article summarizes the strategies we have developed to achieve regioselective C–H functionalizations of isoprene under transition-metal and acid catalysis. 1 Introduction 2 Catalytic Coupling of Indoles with Isoprene 3 Catalytic Coupling of Formaldehyde, Arenes and Isoprene 4 …

The development of new methodologies that enable chemo- and stereoselective construction of fluorinated substituents, such as the trifluoromethyl (CF3) group, plays an essential role in the synthesis of new pharmaceutical agents. The exceptional ability of the CF3 moiety to prevent in vivo metabolism as well as improve other pharmacological properties has led to numerous innovative strategies for installing this unique functional group. One potential yet underdeveloped approach to access these trifluoromethylated products is direct substitution of α-trifluoromethyl carbanions. Although the electron-withdrawing nature of the CF3 group should facilitate deprotonation of adjacent hydrogens, the propensity of the resulting carbanions to undergo α-elimination of fluoride renders this process highly challenging. Herein, we describe a new strategy for stabilizing and utilizing transient α-trifluoromethyl carbanions that …

With chiral 2-methoxy-1-naphthylsulfinyl-based phenyl backbone sulfoxide-olefin ligands, a highly Rh-catalyzed addition of arylboronic acids to N,N-dimethylsulfamoyl-protected aldimines has been developed to afford a broad range of chiral diarylmethylamines in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). Moreover, efficient enantioselective arylation of cyclic N-sulfonylimines was also achieved with excellent enantioselectivities (up to 98% ee).

Catalytic, stereoselective synthesis of skipped dienes is an important topic in organic synthesis. Summarized here are the transition-metal-catalyzed stereoselective approaches and a new, photoinduced stereodivergent strategy reported by our group recently. Our strategy utilizes a synergistic photoredox/nickel protocol to enable the cross-electrophile coupling of allylic carbonates and vinyl triflates to construct 1,4-dienes, the stereoselectivity of which was tuned by the triplet energy (E T) photocatalysts employed, offering a convenient and stereodivergent solution to (E)- and (Z)-1,4-dienes from one set of substrates.

A cooperative catalytic system involving a Pd/XPhos complex and inexpensive 5-norbornene-2-carbonitrile that enables the use of alkyl tosylates as alkylating reagents in the Catellani reaction has been developed. This mild, scalable protocol is compatible with a range of readily available functionalized aryl iodides and alkyl tosylates, as well as terminating olefins (45 examples, up to 97% yield).

Design and exploration of new intermediates for chemo-, regio-, and stereoselective cycloadditions remain a formidable challenge in modern organic synthesis. Compared to the well-developed 1,3-dipolar cycloadditions, Pd-catalyzed1,4-dipolar cycloadditions are generally limited to specialized substrates due to the inherent nature of the thermodynamically driven intramolecular transformations and undesired isomerizations. Herein, we demonstrate the use of ligated palladium catalysts to control and modulate the intermolecular reactivity of aliphatic 1,4-dipoles, enabling two distinctive cycloaddition pathways with a broad scope of acceptors. This atom-economic process also features an eco-friendly in situ deprotonation strategy to generate the corresponding active palladium-mediated dipoles. Overall, a diverse array of chiral 6-membered rings and spiro [2.4] heptanes were prepared in high yield and selectivity …

Troponoid derivatives incorporating imidazolin-2-one moieties were efficiently constructed via a cascade process, under simple thermal conditions, which features a novel nitrogen source, is catalyst- and oxidant-free, and has high atom- and step-economy.

The ProPhenol ligand is a member of the chiral aza‐crown family that spontaneously forms a bimetallic complex upon treatment with alkyl metal reagents, such as Et2Zn and Bu2Mg. The resulting complex features Lewis acidic and Brønsted basic sites, enabling simultaneous activation of both nucleophile and electrophile in the same chiral environment. Since the initial report in 2000, metal‐ProPhenol catalysts have been used to facilitate a broad range of asymmetric transformations, including aldol, Mannich, and Henry reactions, as well as alkynylations and conjugation additions. By promoting such a diverse array of reactions, these complexes provide rapid and atom‐economical access to valuable complex building blocks. In this Review, we describe in detail the development and synthetic applications of these versatile catalysts with a special focus on recent efforts to improve reactivity and selectivity through …

We report herein a simple catalytic method for the extensive labeling of alkenyl C–H bonds through the combination of a palladium(0) complex and a carboxylic acid in the presence of deuterium oxide. The reaction can be applied to a variety of terminal alkenes and the best results are obtained with aryl-substituted examples. This method represents a convenient approach for the preparation of extensively labeled chemicals from the cheapest and safest source of deuterium.

The use of latent nucleophiles, which are molecules that are not nucleophilic but can be activated to act as a nucleophile at an opportune time during the reaction, expands the scope of Lewis base catalyzed reactions. Here, we provide an overview of the concept and show examples of applications to N- and C-centered nucleophiles in allylic substitutions. N- and C-silyl compounds are superior latent (pro)nucleophiles in Lewis base catalyzed reactions with allylic fluorides in which the formation of the strong Si–F bond serves as the driving force for the reactions. The latent (pro)nucleophiles ensure high regioselectivity in these reactions and enable enantioselective transformations of Morita–Baylis–Hillman adducts by the use of common chiral Lewis base catalysts. 1 Introduction 2 Substitution of MBH Carbonates 3 The Concept of Latent (Pro)Nucleophiles 4 Enantioselective Allylation of N-Heterocycles 5 …

A novel Pd0‐catalyzed asymmetric [4+3] annulation reaction of two readily accessible starting materials has been developed for building seven‐membered heterocyclic architectures. The potential [3+2] side pathway could be suppressed though fine tuning of the conditions. A broad scope of cycloaddition donors and acceptors participated in the transformation with excellent chemo‐, regio‐, diastereo‐, and enantioselectivtities, leading to valuable tetrahydroazepines and benzo[b]oxepines.

A novel and highly enantioselective synthesis of hydroxyalkynyl esters and ethers through the asymmetric addition of alkynyl esters or ethers to aldehydes promoted by a cyclopropyl amino alcohol based zinc catalyst has been developed. The method afforded a library of new enantioenriched hydroxyalkynol esters and ethers (up to 93% yield; 95% ee), and it was compatible with a broad range of functional groups. Moreover, it could be used in the synthesis of carbon-chain-elongated enantioenriched hydroxyalkynol esters and (2R,5R)-musclide-A1, a cardiotonic potentiating principle from musk.

An asymmetric phase-transfer-catalyzed N-alkylation of substituted indoles with various Michael acceptors was studied. Acidities of nitroindoles were determined in acetonitrile by UV-Vis spectrophotometric titration. There was essentially no correlation between acidity and reactivity in the aza-Michael reaction. The position of the nitro group on the indole ring was essential to control the stereoselectivity of the reaction. Michael adducts were obtained in high yields and moderate enantioselectivities in the reaction between 4-nitroindole and various Michael acceptors in the presence of cinchona alkaloid based phase-transfer catalysts. In addition to outlining the scope and limitations of the method, the geometries of the transition states of the reaction were calculated.

We disclose our synthetic studies on bilobalide, which features a Diels–Alder reaction of a cyclic anhydride to form two contiguous quaternary carbon centers, desymmetrization of a symmetric diol, and construction of a cyclic acetal under acidic conditions with inversion of configuration at an allylic position.

The SNAr reaction of 1-fluoroxanthone derivatives with alkoxide of 1,1-dimethylallyl alcohol cleanly afforded the corresponding ethers, which have thus far been unavailable. The obtained ethers underwent the Claisen rearrangement at room temperature by treatment with silica gel in toluene. This two-step protocol provides expeditious and high-yield access to xanthones possessing isoprenyl or the related allylic side chain at the C2 position.

An electrochemical sulfonylation reaction of styrenes was developed in which sodium arylsulfinates were used as sulfonylating reagents, a catalytic amount of KI was used as a redox mediator, and Bu4NBF4 was used as the electrolyte. In addition to various styrenes, sodium arylsulfinates with either electron-donating or electron-withdrawing groups were tolerated.

B Using sequential allylic alkylation reactions b to couple a dual electrophile with a dual nucleophile is a powerful way of constructing ring systems. Allylic compounds, cyclization, nucleophilic substitution, synthetic methods, total synthesis.[Extracted from the article]Copyright of Chemistry-A European Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. Copyright applies to all Abstracts.

A transition-metal-free propargylation of ortho-quinone methides (o-QMs) with alkynyl zinc reagents was achieved. A conjugate alkynylation of an o-QM and subsequent cyclization sequence in the presence of KOt-Bu for the synthesis of 2,3-disubstituted benzofurans in one pot was developed. This efficient strategy exhibits good functional-group compatibility and gives moderate to good yields. The present reaction might serve as an attractive method for the synthesis of polysubstituted benzofurans.

Here we briefly reviewed recent synthetic progress toward cytochalasan trimer, asperchalasine A by Tang, Trauner and our group. This process features a highly stereoselective intermolecular Diels–Alder reaction and a HWE or RCM macrocyclization to establish the key monomer aspochalasin B. A late-stage biomimetic oxidative dearomatization of triphenol and subsequent [5+2] cycloaddition cascade furnished asperchalasine A. We anticipate that this key reaction could also be used for the synthesis of other merocytochalasans, and provide some insight into the biosynthetic connections of merocytochalasans. 1 Introduction2 Total Synthesis of Aspochalasin B 3 Total Synthesis of Asperchalasine A 4 Conclusions

The Barbier-type propargylation of azo compounds with α,γ-disubstituted propargylic tosylates was achieved by using metallic barium as the promoter. Various propargylated hydrazines (α-adducts) were exclusively synthesized from the corresponding propargylic tosylates and azobenzenes (diaryldiazenes). The thus-obtained propargylic hydrazines were further efficiently converted into propargylic amines by reductive N–N bond cleavage. Benzidine rearrangement of the propargylic hydrazines was also attempted.

The enantioselective Mannich reaction of 2H-azirines with alkynyl ketones is achieved under Zn-ProPhenol catalysis, delivering various aziridines with vicinal tetrasubstituted stereocenters in high yields with excellent enantioselectivities. The bimetallic Zn-ProPhenol complexes activate both the nucleophile and the electrophile in the same chiral pocket. A unique intramolecular hydrogen bond is observed in the obtained Mannich adducts, which lowers the basicity of the product’s aziridine nitrogen thus favoring enantioselective control and allowing catalyst turnover.

The catalytic asymmetric ring-opening transformations of aziridines represent an important strategy for the construction of various chiral nitrogen-containing molecular architectures. This short review covers the progress achieved in the catalytic asymmetric transformation of racemic aziridines, focusing on the catalytic strategies employed for each different type of such aziridines. 1 Introduction 2 Reaction of Racemic 2-Vinylaziridines 3 Reaction of Racemic 2-Alkylaziridines 3.1 Regiodivergent Parallel Kinetic Resolution 3.2 Kinetic Resolution 4 Reaction of Racemic 2-(Hetero)arylaziridines 4.1 Kinetic Resolution 4.2 Enantioconvergent Transformation 5 Reaction of Racemic Donor–Acceptor-Type Aziridines 6 Conclusion and Outlook

Enantioselective incorporation of trifluoromethyl (−CF3) and trifuoromethylthio (−SCF3) groups in small molecules is of high interest to modulate the potency and pharmacological properties of drug candidates. Herein, we report a Zn-ProPhenol catalyzed diastereo- and enantioselective Mannich addition of α-trifluoromethyl- and α-trifuoromethylthio-substituted ketones. This transformation uses cyclic and acyclic ketones and generates quaternary trifluoromethyl and tetrasubstituted trifuoromethylthio stereogenic centers in excellent yields and selectivities.

A formal synthesis of pseudolaric acid B, a diterpene isolated from the root bark of Pseudolarix kaempferi Gordon (Pinaceae), to Trost’s synthetic intermediate was achieved in 17 steps from a known ketone. Key features of this synthesis include a Claisen rearrangement and iodoetherification to construct quaternary stereocenters and ring-closing metathesis to form the seven-membered ring.

Quaternary carbon stereocenters are ubiquitous in a wide variety of organic compounds and drug molecules. Highly enantioselective construction of such quaternary carbon centers poses a singular challenge due to the steric repulsion between the four different carbon substituents. Herein, we report a novel strategy to control the enantioselective construction of chiral α-quaternary aldehydes from racemic α-branched aldehydes. Distinct from the established chiral α-quaternary aldehyde synthesis, this project employed a chiral π-allyl–Pd complex neighboring the enolate to determine both the enantio- and diastereoselectivity. The synthetic utility of the products has been highlighted by a series of derivatizations, and the potential of this method has been extended to the synthesis of chiral α-quaternary ketones. Furthermore, this reaction exemplifies the themes of step and atom economy, in addition to the principles of …

A nickel(0)-catalyzed intermolecular [3+2] cycloaddition of bis(alkylidenecyclopropanes) with diazenes such as diethyl or diisopropyl azodicarboxylate gave pyrazolidine-1,2-dicarboxylates in moderate to good yields (61–72%).

The development of the palladium-catalyzed allylic alkylation of in situ generated boron enolates via tandem 1,4-hydroboration is reported. Investigation of the reaction revealed insights into specific catalyst electronic features as well as a profound leaving group effect that proved crucial for achieving efficient allylic alkylation of ester enolates at room temperature and ultimately a highly preparatively useful synthesis of notoriously challenging acyclic all-carbon quaternary stereocenters. The method demonstrates boron enolates as viable pro-nucleophiles in transition-metal catalyzed allylic alkylation, potentially opening up further transformations outside their traditional use.

A series of new dihydrobenzooxophosphole-based Lewis base organocatalysts were designed and synthesized. They are shown to be effective in trichlorosilane-mediated stereoselective conjugate reductions of C=C bonds. DFT calculations reveal that the strong hydrogen bonds between the amide linker and the chloride on silicon in the transition state contribute to the high reactivity of the catalyst.

An efficient, novel photocatalyzed allylic-alkynylation methodology via copper-based cross-dehydrogenative coupling (CDC) is described. Different types of 1,4-enyne compounds were synthesized in one step at room temperature using copper(I) terpyridyl complex as photocatalyst/initiator. This procedure is an improvement and to some extent complementary to previously reported thermal CDC methods. Preliminary investigations on the reaction mechanism are also presented.

Metal-vinylidenes, generated by treatment of terminal alkynes with transition metals, are very useful intermediates in modern synthetic chemistry as shown by the high number of transformations in which they are involved. When a metal-vinylidene is generated in the presence of an oxidant, its immediate oxidation to a ketene occurs. In this short review, recent synthetic applications of the oxidation of alkynes via ketene intermediates from initially formed metal-vinylidenes are highlighted. 1 Introduction 2 Oxidation of Metal-Vinylidenes with Internal Oxidants 3 Oxidation of Metal-Vinylidenes with External Oxidants 4 Conclusions

Metal‐catalyzed allylic alkylation reactions between dual nucleophiles and dual electrophiles represent a powerful set of methods for the synthesis of small‐, medium‐, and even large‐sized rings. Using this strategy, a handful of simple allylic diol derivatives can be transformed into a broad array of complex carbo‐ and heterocycles of varying ring sizes in just a single step. Because of their ability to rapidly generate complexity, annulative allylic alkylation reactions between dual nucleophiles and dual electrophiles have been extensively employed in the total synthesis of both natural products and pharmaceutical compounds.

Chiral secondary mixed alkylcopper-zinc reagents were prepared from the corresponding alkyl iodides and reacted with allylic epoxides via an anti-SN2′-substitution and retention of configuration of the chiral alkylorganometallic, leading to chiral allylic alcohols. This method was used in a total synthesis of the natural product (3S,6R,7S)-zingiberenol in 8 steps and 9.7% overall yield [dr (3S,6R) = 99:1; dr (6R,7S) = 81:19] starting from commercially available 3-methyl-2-cyclohexenone.

A wide range of α-diazo-β-ketosulfones have been applied to thermally promoted tandem Wolff rearrangement – Staudinger [2+2] cycloaddition with imines to give polysubstituted β-lactam sulfones. Diastereomerically pure syn-diastereomers were obtained in good yields and the relative stereochemistry was confirmed by single-crystal X-ray crystallography. These findings significantly expand the scope of this transformation, in contrast to substantial limitations reported previously. Moreover, this methodology enables flexible exploration of new substitution patterns around the privileged β-lactam core for drug design and optimization.

A new protocol for the controlled reduction of nitriles to aldehydes was developed using a combination of sodium hydride and zinc chloride. The iminyl zinc intermediates derived from aromatic nitriles could be further functionalized with allylmetal nucleophiles to afford homoallylamines. As the method allows the reduction of various aliphatic and aromatic nitriles with a concise procedure under milder reaction conditions and exhibits wide functional group compatibility, it is well suited for use in various opportunities in chemical synthesis.

Singh’s catalyst has emerged as one of the most promising and valuable catalysts in the field of asymmetric synthesis. Since its discovery, it has proven to be one of the best organocatalysts for asymmetric direct aldol reactions, and is equally efficient in aqueous and organic media. In this Short Review, we summarize reactions utilizing Singh’s catalyst under various conditions. 1 Introduction 2 Synthesis of Singh’s Catalyst 3 Applications in Asymmetric Synthesis 4 Conclusion

Whereas metal-mediated cross-couplings find broad applications in syntheses of medicines, agrochemicals, and natural products, these powerful transformations have limited utility for Lewis basic substrates (e.g., heteroarenes), wherein basic functionalities coordinate to the metal center, hindering product formation. In this context, we have developed a transition-metal-free cross-coupling reaction mediated by sulfur(IV). This method leverages the ability of simple alkyl sulfinyl(IV) chlorides to form bipyramidal sulfurane complexes to drive a pseudo ‘reductive elimination’ process from the hypervalent sulfur atom, thereby readily providing unsymmetrical biheteroarenes. 1 Introduction 2 Historical Sulfurane(IV)-Mediated Couplings 3 Unsymmetrical Heterocycle Cross-Couplings 4 Conclusion

Nature’s synthetic plans to construct molecules have been developed over millions of years of evolution and frequently prove to be among the most sophisticated. Mimicking nature’s route can be a direct and feasible way for synthetic organic chemists to construct complicated molecules. However, lacking nature’s ability to manipulate enzymes often prevents us from reproducing the same route. Modifying nature’s approaches can provide a simpler synthetic alternative to access complex structural target molecules. Here we report a strategy that simplifies the synthesis of terpenes by inverting the order of nature’s two-phase biosynthesis route. We first unite simple molecules into a polyfunctionalized linear polyenyne, with all the desired carbons and oxygens in the targeted places. This compound then undergoes polyenyne cycloisomerization, in the presence of all the functional groups, to give polyoxidized terpenes …

An iodobenzene-catalyzed oxidative cyclization of Michael adducts of activated methylene compounds with nitroolefins or chalcones is developed. mCPBA is used as oxidant together with Bu4NI for the generation of a highly reactive iodine(III) species to mediate the cyclopropanation via a ligand exchange and reductive elimination process. A range of highly functionalized cyclopropanes are synthesized with high diastereoselectivities.

Trost and Min report a novel palladium-catalyzed cyclization reaction enabling the synthesis of intermediate F. Elaboration of the common precursor furnishes an array of natural products, including (+)-conocenolide E.

ConspectusEnolate chemistry is one of the most fundamental strategies for the formation of carbon–carbon and carbon–heteroatom bonds. Classically, this has been accomplished through the use of stoichiometric quantities of strong base and cryogenic reaction temperatures. However, these techniques present issues related to enolate regioselectivity and functional group tolerance. While more modern methods utilizing stoichiometric activating agents have overcome some of these limitations, these processes add additional steps and suffer from poor atom economy. While certain classes of highly acidic nucleophiles have enabled the development of elegant and general catalytic solutions to address all of these limitations, functionalizing less acidic nucleophiles remains difficult.To overcome these challenges, we developed an alternative general approach for the formation and subsequent functionalization of …

Metal-catalyzed allene cycloisomerizations provide rapid entry into five-membered carbocyclic frameworks, a common motif in natural products and pharmaceuticals. While both Au(I) and Pd(0)-catalyzed allene cycloisomerizations give 5-endo-dig cyclization, Pd prefers the syn diastereomer in contrast to the anti isomer observed with Au. The change in stereoselectivity is proposed to arise from buildup of A1,3 strain during the key carbopalladation step to furnish the cycloisomerized products in moderate to good dr with yields comparable to Au(I) catalysts.

A novel disulfenylation of alkenes with thiophenols and their corresponding disulfides by using air as the oxidant has been achieved. This transformation provides a facile and practical protocol for the synthesis of vicinal dithioethers under mild conditions.

For the first time, azaoxyallyl cations were used as cycloaddition partners with tropone derivatives to access nitrogen-containing [7,6]-fused bicycles in a metal-free process under mild reaction conditions. DFT computations have been used to shed light on the selectivities observed during the course of the reaction.

Significance: Trost and co-workers report a ruthenium-catalyzed multicomponent synthesis of the 1, 3-dienyl-6-oxy polyketide motif. Unsymmetrical 3-boryl-1, 4-diene reagents undergo highly diastereoselective allylations in the presence of carbonyl compounds, providing the desired products in good yields.Comment: The authors demonstrated an efficient methodology to form three contiguous sp3 stereocenters with high stereoselectivity in a single operation. Furthermore, the described 3-boryl-1, 4-diene products can be considered as useful building blocks beyond the addition to carbonyl compounds.

Herein we present a Zn-ProPhenol-catalyzed double Mannich reaction between ynones and imines that generates 1,3-diamines in excellent yield as well as diastereo- and enantioselectivity (>99.5% ee). With 2.2 equiv of a single imine electrophile, we obtain pseudo-symmetrical diamines whereas, with two different imine partners, we obtain unsymmetrically substituted 1,3-diamines with three contiguous stereocenters. In addition, we showcase the utility of these double Mannich adducts by transforming the 1,3-diamine motif into a variety of interesting products.

The ruthenium catalytic addition of alkenes to alkynes has been demonstrated as a powerful synthetic tool to form diene motifs and widely applied in the synthesis of complex molecules. However, except for the intramolecular coupling, trisubstituted alkenes are unsatisfactory coupling partners with alkynes, presumably due to the increased steric hindrance. Herein, we discovered that substituted vinyl 1,2-bisboronate derivatives can serve as the trisubstituted alkene equivalents to couple with alkynes, generating various boryl-substituted homoallylic alcohol motifs with good stereoselectivity through the sequential allylboration with aldehydes. In contrast to carbon substituents on the double bond, boron substituents accelerate the alkyne coupling.

2-Azaallyl anions are valuable intermediates which have versatile applications in functionalization with various electrophiles. Decarboxylation of the imines formed from aromatic aldehydes and α,α-diphenylglycine provides an interesting and efficient way to generate delocalized 2-azaallyl anions, which display high reactivity toward different electrophiles with excellent regioselectivity at the diphenylketimino aryl carbon of the 2-azaallyl anions. The transformation produces various amines in good yields under very mild conditions. This Synpacts article highlights the recent advances on the decarboxylative umpolung synthesis of amines from carbonyl compounds. 1 Introduction 2 Decarboxylative Umpolung Reactions of Carbonyl Compounds with Different Electrophiles 2.1 Reaction with π-Allyl–Pd(II) Species 2.2 Reaction with Morita–Baylis–Hillman Adducts 2.3 Reaction with Imines 2.3.1 Intermolecular …

In this Account, we describe our studies on the total synthesis of several natural products using intramolecular Nozaki–Hiyama–Takai–Kishi (NHTK) reactions. In each synthesis, an NHTK reaction is used to efficiently construct a medium-sized ring. These examples demonstrate the utility of the intramolecular NHTK reaction in natural product synthesis. 1 Introduction 2 Total Synthesis of (+)-Pestalotiopsin A 3 Total Synthesis of (+)-Cytosporolide A 4 Total Synthesis of (+)-Vibsanin A 5 Total Syntheses of (+)-Aquatolide and Related Humulanolides 6 Conclusion

A new efficient method for the synthesis of a high ratio of E-alkenes from E/Z mixtures of alkenes with B2pin2 in the presence of a rhodium catalyst is described. This reaction features mild reaction conditions, broad functional group tolerance, and highly great application potential.

Cobalt(III)-catalyzed electrophilic amination of inert C(sp3)–H bonds of weakly coordinating thioamides with readily accessible anthranil derivatives was accomplished under mild conditions, with good functional group tolerance, thus providing various amino aldehydes and amino ketones. Moreover, our protocol with the versatile [Cp*Co(MeCN)3][SbF6]2 features excellent atom-economy and oxidant-free conditions, and allows facile late-stage functionalization.

Bryostatins are a family of 21 complex marine natural products with a wide range of potent biological activities. Among all the 21 bryostatins, bryostatin 3 is structurally the most complex. Whereas nine total syntheses of bryostatins have been achieved to date, bryostatin 3 has only been targeted once and required the highest number of steps to synthesize (43 steps in the longest linear sequence and 88 total steps). Here, we report a concise total synthesis of bryostatin 3 using 22 steps in the longest linear sequence and 31 total steps through a highly convergent synthetic plan by the use of highly atom-economical and chemoselective transformations in which alkynes played a major role in reducing step count.

A base-promoted direct synthesis of sulfinates from N-sulfonylhydrazones is described. Various N-sulfonylhydrazones, derived from aldehydes and ketones, are converted into the corresponding sulfinates in moderate to good yields. This protocol possesses many advantages such as readily available and stable starting materials, broad substrate scope, and metal-free reaction conditions.

A diastereoselective palladium-catalyzed dearomative formal (4+2) cycloaddition between vinyl benzoxazinanones and 3-nitroindoles has been developed. This reaction provides a concise route to tetrahydro-5H-indolo[2,3-b]quinolines in excellent yield (up to 94%) and diastereoselectivity (up to >98:2), with versatile functional handles including vinyl, nitro, and free NH groups.

A new ruthenium-based catalytic system for branched-selective asymmetric allylic alkylation is disclosed and applied to the synthesis of chiral isatin derivatives. The catalyst, which is generated in situ from commercially available CpRu(MeCN)3PF6 and a BINOL-derived phosphoramidite, is both highly active (TON up to 180) and insensitive to air and moisture. Additionally, the N-alkylated isatins accessible using this methodology are versatile building blocks that are readily transformed into chiral analogs of achiral drug molecules.

Polyketide natural products are an important class of biologically active compounds. Although substantial progress has been made on the synthesis of repetitive polyketide motifs through the iterative application of a single reaction type, synthetic access to more diverse motifs that require more than one type of carbon–carbon bond connection remains a challenge. Here we describe a catalytic, multicomponent method for the synthesis of the privileged polyketide 1,3-dienyl-6-oxy motif. The method allows for the formation of two new carbon–carbon bonds and two stereodefined olefins. It generates products that contain up to three contiguous sp3 stereocentres with a high stereoselectivity in a single operation and can be used to generate chiral products. The successful development of this methodology relies on the remarkable efficiency of the ruthenium-catalysed alkene–alkyne coupling reaction between readily …

Genetic screens in cultured human cells represent a powerful unbiased strategy to identify cellular pathways that determine drug efficacy, providing critical information for clinical development. We used insertional mutagenesis-based screens in haploid cells to identify genes required for the sensitivity to lasonolide A (LasA), a macrolide derived from a marine sponge that kills certain types of cancer cells at low nanomolar concentrations. Our screens converged on a single gene, LDAH, encoding a member of the metabolite serine hydrolase family that is localized on the surface of lipid droplets. Mechanistic studies revealed that LasA accumulates in lipid droplets, where it is cleaved into a toxic metabolite by LDAH. We suggest that selective partitioning of hydrophobic drugs into the oil phase of lipid droplets can influence their activation and eventual toxicity to cells.

The cyclopropane functionality has been exploited in a myriad of settings that range from total synthesis and methodological chemistry, to medical and materials science. While it has been seen in such a breadth of settings, the typical view of the cyclopropane moiety is that its reactivity is derived primarily from the release of ring strain. While this simplified view is a useful shorthand, it ignores the specific nature of cyclopropyl molecular orbitals. This review aims to present the different facets of cyclopropane bonding by examining the main models that have been used to explain the reactivity of the functionality over the years. However, even with advanced theory, being able to precisely predict the reactivity of an exact system is nigh impossible. Specifically chosen, carbonyl-bearing cyclopropyl species act as so-called acceptor cyclopropanes and, if correctly derivatised, donor–acceptor cyclopropanes. By undertaking …

A concise and modular asymmetric synthesis of the calcium channel blocker (S)-verapamil is described. This approach employs an enantioselective rhodium-catalyzed allylic alkylation reaction between an α-isopropyl-substituted benzylic nitrile and allyl benzoate to construct the challenging acyclic quaternary stereocenter. The terminal olefin then serves as a convenient synthetic handle for a hydroamination to introduce the phenethylamine moiety, furnishing (S)-verapamil in three steps and 55% overall yield, thus providing the most efficient synthesis of this important pharmaceutical reported to date. Furthermore, given the modular nature of the synthesis, it can be readily modified to prepare structurally related bioactive agents.

The preparation of acyclic β‐fluoro amines bearing tetrasubstituted fluorine stereocenters is described via a direct Zn/ProPhenol‐catalyzed Mannich reaction. The reaction utilizes branched vinyl or alkynyl α‐fluoro ketones that can be coupled with a range of aryl, heteroaryl, vinyl, or cyclopropyl aldimines in high yield and with excellent diastereo‐ (up to >20:1) and enantioselectivity (up to 99 %). The use of readily cleaved tert‐butoxycarbonyl (Boc) or carboxybenzyl (Cbz) imine protecting groups adds utility to the reaction by allowing for easy access to the free amine products under mild and chemoselective reaction conditions.

Significance: Lasonolide A (LasA) is a polyketide macrolide with potent cytotoxic activity. Its unique activity profile against the NCI-60 cell panel made it an intriguing candidate for development as an anticancer therapeutic agent. The mechanism of action for its cytotoxicity is complex and poorly understood. Here, Rohatgi and co-workers unravel a key step in the mechanism of action of LasA, which may have implications in future drug design.Comment: The total synthesis of LasA and several analogues was described previously (J. Am. Chem. Soc. 2016, 138, 11690). Insertional mutagenesis of HAP1 cells identified the serine hydrolase LDAH (lipid droplet associated hydrolase) as critical to LasA cytotoxicity. Mechanistic studies revealed that LasA accumulates in the endoplasmic reticulum and in lipid droplets. There, membrane-bound LDAH cleaves the LasA side-chain ester, converting it into LasF, which is the true …

A base-promoted (2+4) annulation of benzofuran-derived azadienes with para-quinone methide derivatives has been established, which afforded spiro-benzofuran derivatives in generally high yields (57–97%) and with good diastereoselectivities (85:15 to >95:5 dr). This reaction not only represents the first application of benzofuran-derived azadienes as two-carbon building blocks in annulations, but also provides an efficient protocol for the construction of spiro-benzofuran scaffolds with chemoselectivity and high diastereoselectivity. This approach will enrich the chemistry of benzofuran-derived azadiene-involved reactions.

The highs, lows, and diversions of a journey leading to two syntheses of 6,7-dideoxysqualestatin H5 is described. Both syntheses relied on highly diastereoselective n-alkylations of a tartrate acetonide enolate and subsequent oxidation–hydrolysis to provide an asymmetric entry to β-hydroxy-α-ketoester motifs. The latter were differentially elaborated to diazoketones which underwent stereo- and regioselective Rh(II)-catalysed cyclic carbonyl ylide formation–cycloaddition and then acid-catalysed transketalisation to generate the 2,8-dioxabicyclo[3.2.1]octane core of the squalestatins/zaragozic acids at the correct tricarboxylate oxidation level. The unsaturated side chain was either protected with a bromide substituent during the transketalisation or introduced afterwards by a stereoretentive Ni-catalyzed Csp3–Csp2 cross-electrophile coupling. 1 Introduction   2 Racemic Model Studies to the Squalestatin/Zaragozic …

Erythrina alkaloids were identified at the end of the 19th century and today, more than 100 members of the erythrinane family have been isolated. They are characterized by a unique tetracyclic, α-tertiary spiroamine scaffold. Herein we detail our efforts towards the development of a divergent enantioselective synthesis of (+)-dihydro-β-erythroidine (DHβE) – one of the most prominent members of this intriguing family of natural products. 1 Introduction 2 Synthetic Strategy 2.1 First Generation 2.2 Second Generation 2.3 Third Generation 2.3.1 Radical Endgame 2.3.2 Completion of the Total Synthesis 3 Conclusion

The efficient and selective synthesis of functionalized seven‐membered rings remains an important pursuit within synthetic organic chemistry, as this motif appears in numerous drug‐like molecules and natural products. Use of cycloaddition reactions remains an attractive approach for their construction within the perspective of atom and step economy. Additionally, the ability to combine multiple components in a single reaction has the potential to allow for efficient combinatorial strategies of diversity‐oriented synthesis. The inherent entropic penalty associated with achieving these transformations has impressively been overcome with development of catalysis, whereby the reaction components can be pre‐organized through activation by transition‐metal‐catalysis. The fine‐tuning of metal/ligand combinations as well as reaction conditions allows for achieving chemo‐, regio‐, diastereo‐ and enantioselectivity in …

Significance: Trost and Gnanamani report a mild and highly selective Zn-ProPhenol-catalyzed double Mannich reaction employing imines and ynones as the reactive partners. The reaction allows access to highly functionalized 1, 3-diamines under mild conditions in excellent yields, with high diastereo-and enantioselectivity, even at gram scale.

We report a facile synthesis of sulfones, β-keto sulfones, and sulfonamides from vinyl sulfones via an addition–elimination sequence where in situ generation of nucleophilic sulfinate ion is mediated by cyanide. The use vinyl sulfones renders high selectivity for S-alkylation to produce sulfones in high yields. In the presence of N-bromosuccinimide, primary and secondary amines underwent sulfonamide formation. A preliminary mechanistic study showed the formation of acrylonitrile as an innocent byproduct, without interfering with the desired reaction pathway while generating a sulfinate nucleophile.