Toward a symphony of reactivity: cascades involving catalysis and sigmatropic rearrangements

Repurposing myoglobin into a carbene transferase for a [2,3]-sigmatropic Sommelet-Hauser rearrangement

New-to-Nature biocatalysis has emerged as a promising tool in organic synthesis thanks to progress in protein engineering. Notably, hemeproteins have been evolved into robust catalysts for carbene and nitrene transfers and related sigmatropic rearrangements. In this work, we report the first example of a [2,3]-sigmatropic Sommelet-Hauser rearrangement initiated by a carbene transfer of the sperm whale myoglobin mutant L29S,H64V,V68F that was previously reported to catalyze the mechanistically similar [2,3]-sigmatropic Doyle-Kirmse rearrangement. This repurposed heme enzyme catalyzes the Sommelet-Hauser rearrangement between ethyl diazoacetate and benzyl thioethers bearing strong electron-withdrawing substituents with good yields and enantiomeric excess. Optimized catalytic conditions in the absence of any reductant led to an increased asymmetric induction with up to 59% enantiomeric excess. This myoglobin mutant is therefore one of the few catalysts for the asymmetric Sommelet-Hauser rearrangement. This work broadens the scope of abiological reactions catalyzed by iron-carbene transferases with a new example of asymmetric sigmatropic rearrangement.

Approach to the Core Structure of Signermycin B

Among the natural tetramic acids with a decalinoyl part, signermycin B is unique because it contains a cis-decalin. In this paper, we demonstrate that the cis-decalin section of signermycin B can be accessed by an anionic oxy-Cope rearrangement. The substrate, a tricyclic dienol was prepared by an intramolecular Diels-Alder reaction of a masked ortho-benzoquinone, generated by oxidation of an α-methoxyphenol in presence of cis-2-hexenol. After a superfluous bromine on the cycloadduct was removed, reaction of the tricyclic ketone with isopropenylmagnesium bromide led to the tricyclic trienol that underwent the oxy-Cope rearrangement to a cis-decalinone. While we could show, that introduction of the 4-ethyl substituent (signermycin B numbering) is possible by enolate alkylation, the 4-epi-isomer was formed.

Gold-Catalyzed Arylative Cope Rearrangement

Cope rearrangements have garnered significant attention owing to their ability to undergo structural reorganization in stereoselective manner. While substantial advances have been achieved over decades, these rearrangements remained applicable exclusively to parent 1,5-hexadienes. Herein, we disclose the gold-catalyzed arylative Cope rearrangement of 1,6-heptadienes via a cyclization-induced [3,3]-rearrangement employing ligand-enabled gold redox catalysis. Detailed mechanistic investigations including several control experiments, cross-over experiment, HRMS analysis, 31P NMR and DFT studies have been performed to underpin the mechanism.

Enantioselective Formal 1,2-Diamination of Ketenes with Iminosulfinamides: Asymmetric Synthesis of Unnatural α,α-Disubstituted α-Amino Acid Derivatives

A method was developed for the enantioselective formal 1,2-diamination of disubstituted ketenes using iminosulfinamides as nitrogen sources. The protocol involves the addition of lithium iminosulfinamides to ketenes to form N-iminosulfinyl amide metalloenolates. These metalloenolates then undergo a [2,3]-sigmatropic rearrangement to yield unnatural α,α-disubstituted α-amino acid derivatives with high enantiopurity. The chirality present at the sulfur atom in the iminosulfinamides is effectively transferred to α carbon of the resulting products, facilitating the highly enantioselective amination of ketenes.

Toward Efficient and Stereoselective Aromatic and Dearomative Cope Rearrangements: Experimental and Theoretical Investigations of α-Allyl-α'-Aromatic γ-Lactone Derivatives

The aromatic Cope rearrangement is an elusive transformation that has been the subject of a limited number of investigations compared to those seemingly close analogues, namely the Cope and aromatic Claisen rearrangement. Herein we report our investigations inspired by moderate success observed in the course of pioneering works. By careful experimental and theoretical investigations, we demonstrate that key substitutions on 1,5-hexadiene scaffold allow fruitful transformations. Especially, efficient functionalisation of the heteroaromatic rings results from the aromatic Cope rearrangement, while highly stereoselective interrupted aromatic Cope rearrangements highlight the formation of chiral compounds through a dearomative process.

Photosensitization enables Pauson-Khand-type reactions with nitrenes

The Pauson-Khand reaction has in the past 50 years become one of the most common cycloaddition reactions in chemistry. Coupling two unsaturated bonds with carbon monoxide, the transformation remains limited to CO as a C1 building block. Herein we report analogous cycloaddition reactions with nitrenes as an N1 unit. The reaction of a nonconjugated diene with a nitrene precursor produces bicyclic bioisosteres of common saturated heterocycles such as piperidine, morpholine, and piperazine. Experimental and computational mechanistic studies support relaying of the diradical nature of triplet nitrene into the π-system. We showcase the reaction's utility in late-stage functionalization of drug compounds and discovery of soluble epoxide hydrolase inhibitors.

Stereospecific Synthesis of Cyclohexenone Acids by [3,3]-Sigmatropic Rearrangement Route

Herein we report a modular synthetic method for the preparation of diaryl-substituted cyclohexenone acids starting from phenyl pyruvate and suitable enones. When the reaction is carried out in alkaline tert-butanol or toluene solutions in microwave-assisted conditions mainly anti configuration products are obtained with up to 86% isolated yield. However, when the reaction is carried out in alkaline water, a mixture of products with anti and syn conformations is obtained with up to 98% overall isolated yield. Mechanistically the product with anti conformation forms by a hemiketal-oxy-Cope type [3,3]-sigmatropic rearrangement-intramolecular aldol condensation route and syn product by an intermolecular aldol condensation-electrocyclization (disrotatory type) route.

Diastereo- and Enantioselective Synthesis of Functionalized Dihydropyrans via an Organocatalytic Claisen Rearrangement/Oxa-Michael Addition Tandem Sequence

A straightforward diastereo- and enantioselective Claisen rearrangement/oxa-Michael addition tandem sequence with a cinchona squaramide catalyst was described, which afforded a practical and atom-economical approach to access a range of valuable dihydropyrans in good to excellent yields with excellent stereoselectivities. The organo-bifunctional catalyst played a key role in enhancing stereoselectivity in this asymmetric tandem sequence. Moreover, the asymmetric catalytic sequential processes of the hydroalkoxylation/Claisen rearrangement/cyclization sequence and Claisen rearrangement/aza-Michael addition tandem sequence have also been afforded good yields and moderate stereoselectivities.

Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes To Form Semibullvalene

We describe the various escape channels available to dirhodium carbene intermediates from cycloheptatrienyl diazo compounds located with density functional theory. An intramolecular cyclopropanation would, in principle, provide a new route to semibullvalenes (SBVs). A detailed exploration of the potential energy surface reveals that methylating carbon-7 suppresses a competing β-hydride migration pathway to heptafulvene products, giving SBV formation a reasonable chance. During our explorations, we additionally discovered unusual spirononatriene, spironorcaradiene, and metal-stabilized 9-barbaralyl cation structures as local minima.

An Organocatalytic Oxy-Cope/Michael Cascade Reaction

Ethyl diazepane carboxylate catalyzes the oxy-Cope rearrangement of 4-hydroxy- and 4-alkoxy-1,5-hexadiene-2-carboxaldehydes via iminium ion activation. The resulting intermediate undergoes an intramolecular Michael reaction to furnish cyclopentane-containing products. The reaction proceeds with a range of substrates, including both cyclic and acyclic substrates, and tolerates substitution on the vinyl substituent. Substrates fused on a cycloalkane framework undergo net ring expansion/cyclopentannulation with a high degree of stereocontrol via chairlike transition states. The reaction extends iminium organocatalysis to the oxy-Cope rearrangement, embedded within a complexity-generating cascade transformation.

[3,3]-Sigmatropic Rearrangements of Naphthyl 1-Propargyl Ethers: para-Propargylation and Catalytic Asymmetric Dearomatization

The para-Claisen rearrangement of aryl 1-propargyl ethers involves two-step [3,3]-sigmatropic rearrangements and dearomatization process, which has high activation barriers and is of challenge. Here we discovered thermal para-Claisen rearrangement of naphthyl 1-propargyl ethers, and it enabled the formation of formal para-C-H propargylation products upon rearomatization. Chirality transfer occurred if optically active propargyl ethers were employed, leading to the construction of aryl/propargyl-containing stereogenic centers. Moreover, catalytic asymmetric dearomatization of naphthyl 1-propargyl ethers with different substitution at para-position gave access to benzocyclohexenones bearing all-carbon quaternary stereocenters. The reaction was accelerated by a chiral N,N'-dioxide/Co(OTf)₂ complex catalyst to achieve high yields (up to 98 %) and high enantioselectivities (up to 93 % ee). The DFT calculations and experimental results provided important clues to clarify the para-Claisen rearrangement process as well as the chiral induction and remote delivery.

Recent advances in metal-catalysed asymmetric sigmatropic rearrangements

Asymmetric sigmatropic rearrangement is a powerful organic transformation via substrate-reorganization to efficiently increase molecular complexity from readily accessible starting materials. In particular, a high level of diastereo- and enantioselectivity can be readily accessed through well-defined and predictable transition states in [3,3], [2,3]-sigmatropic rearrangements, which have been widely applied in the synthesis of various chiral building blocks, natural products, and pharmaceuticals. In recent years, catalytic asymmetric sigmatropic rearrangements involving chiral metal complexes to induce stereocontrol have been intensively studied. This review presents an overview of metal-catalysed enantioselective versions of sigmatropic rearrangements in the past two decades, mainly focusing on [3,3], [2,3], and [1,3]-rearrangements, to show the development of substrate design, new catalyst exploitation, and novel cascade processes. In addition, their application in the asymmetric synthesis of complex natural products is also exemplified.

Ring contraction in synthesis of functionalized carbocycles

Carbocycles are a key and widely present structural motif in organic compounds. The construction of structurally intriguing carbocycles, such as highly-strained fused rings, spirocycles or highly-functionalized carbocycles with congested stereocenters, remains challenging in organic chemistry. Cyclopropanes, cyclobutanes and cyclopentanes within such carbocycles can be synthesized through ring contraction. These ring contractions involve re-arrangement of and/or small molecule extrusion from a parental ring, which is either a carbocycle or a heterocycle of larger size. This review provides an overview of synthetic methods for ring contractions to form cyclopropanes, cyclobutanes and cyclopentanes en route to structurally intriguing carbocycles.

Recent developments in one-pot stepwise synthesis (OPSS) of small molecules

One-pot synthesis is an active topic in organic chemistry due to its intrinsic advantages of simple operation, high mass efficiency, low cost, and less amount of waste disposal. Among three kinds of one-pot syntheses, 1) cascade reactions, 2) multicomponent reactions (MCRs), and 3) one-pot stepwise synthesis (OPSS), OPSS could be more flexible and practical since it is carried out stepwisely and have variable reaction conditions for different steps. This perspective article uses selected examples to highlight the recent development in OPSS involving cyclization, cycloaddition, rearrangement, and catalytic reactions for the synthesis of heterocyclic scaffolds, asymmetric molecules, natural products, and bioactive compounds.

Advancing the Logic of Polymer Synthesis via Skeletal Rearrangements

Polymers are ubiquitous materials that have driven technological innovation since the middle of the 20th century. As such, the logic that guides polymer synthesis merit considerable attention. Thus far, this logic has often been ‘forward-synthetic’, which constrains the accessible structures of polymer materials. In this article, we emphasize the benefits of ‘retrosynthetic’ logic and posit that the development of skeletal rearrangements of polymer backbones is central to the realization of this logic. To illustrate this point, we discuss two recent examples from our laboratory – Brook and Ireland–Claisen rearrangements of polymer backbones – and contextualize them in prior reports of sigmatropic rearrangements and skeletal rearrangements of polymers. We envision that further development of skeletal rearrangements of polymers will enable advances in not only the chemistry of such rearrangements and the logic of polymer synthesis, but also polymer re- and upcycling.

Quaternary Ammonium Ion-Tethered (Ambient-Temperature) HDDA Reactions

The hexadehydro-Diels-Alder (HDDA) reaction converts a 1,3-diyne bearing a tethered alkyne (the diynophile) into bicyclic benzyne intermediates upon thermal activation. With only a few exceptions, this unimolecular cycloisomerization requires, depending on the nature of the atoms connecting the diyne and diynophile, reaction temperatures of ca. 80-130 °C to achieve a convenient half-life (e.g., 1-10 h) for the reaction. In this report, we divulge a new variant of the HDDA process in which the tether contains a central, quaternized nitrogen atom. This construct significantly lowers the activation barrier for the HDDA cycloisomerization to the benzyne. Moreover, many of the ammonium ion-based, alkyne-containing substrates can be spontaneously assembled, cyclized to benzyne, and trapped in a single-vessel, ambient-temperature operation. DFT calculations provide insights into the origin of the enhanced rate of benzyne formation.

The pinene scaffold: its occurrence, chemistry, synthetic utility, and pharmacological importance

Plant-based secondary metabolites have been a major source of drug discovery and inspiration for new generations of drugs. Plants offer a wide variety of compound classes, including alkaloids, terpenes, flavonoids, and glycosides, with different molecular architectures (fused bridgehead, bi- and polycyclic, spirocyclic, polycyclic, and acyclic). The diversity, abundance, and accessibility of plant metabolites make plants an attractive source of human and animal medicine. Even though the pinene scaffold is abundant in nature and has historical use in traditional medicine, pinene and pinene-derived compounds have not been comprehensively studied for medicinal applications. This review provides insight into the utility of the pinene scaffold as a crucial building block of important natural and synthetic products and as a chiral reagent in the asymmetric synthesis of important compounds.

Energy Transfer Photocatalytic Radical Rearrangement in N-Indolyl Carbonates

A new type of sp³-like N-centered radical has been generated by selective energy transfer catalysis. Upon photoexcitation, homolytic N-O bond cleavage of N-indolyl carbonate in the presence of an Ir complex produced N- and O-centered radicals. The high spin density at the C3 position of indole led to radical recombination with the O-centered radical, affording valuable 3-oxyindole derivatives without decarboxylation. Transformations of the desired products into various molecules were also demonstrated.

An amine template strategy to construct successive C-C bonds: synthesis of benzo[h]quinolines by a deaminative ring contraction cascade

We developed a convergent strategy to build, cyclize and excise nitrogen from tertiary amines for the synthesis of polyheterocyclic aromatics. Biaryl-linked azepine intermediates can undergo a deaminative ring contraction cascade reaction, excising nitrogen with the formation of an aromatic core. This strategy and deaminative ring contraction reaction are useful for the synthesis of benzo[h]quinolines.

Yb(OTf)3 catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles

A Yb(OTf)₃ catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles was achieved, affording a variety of multifunctional 3-ylideneoxindoles with good yields and Z/E selectivities (64%-89% yield, 78 : 22->99 : 1 Z/E). Importantly, an operationally simple, one-pot sequential catalytic synthesis of 3-ylideneoxindoles was also developed. Additionally, a cross [1,3]-rearrangement experiment and nonracemic transformation were also carried out, which indicated a concerted rearrangement mechanism of this methodology.

Copper-Catalyzed Asymmetric Diyne Cyclization via [1,2]-Stevens-Type Rearrangement for the Synthesis of Chiral Chromeno[3,4-c]pyrroles

Here, we report a copper-catalyzed asymmetric cascade cyclization/[1,2]-Stevens-type rearrangement via a non-diazo approach, leading to the practical and atom-economic assembly of various valuable chiral chromeno[3,4-c]pyrroles bearing a quaternary carbon stereocenter in generally moderate to good yields with wide substrate scope and excellent enantioselectivities (up to 99 % ee). Importantly, this protocol not only represents the first example of catalytic asymmetric [1,2]-Stevens-type rearrangement based on alkynes but also constitutes the first asymmetric formal carbene insertion into the Si-O bond.

Triaminocyclopentadienyl Ruthenium Complexes - New Catalysts for Cascade Conversions of Propargyl Alcohols

Various triaminocyclopentadienyl ruthenium complexes have been synthesized from Ru₃ (CO)₁₂ . The new complexes were tested for their ability to catalyze cascade conversions of propargyl alcohols. Their associated catalytic activities complement the activities of known diaminocyclopentadienone ruthenium complexes. In particular, the substrate scope of catalytic cycloadditions with 3-ketolactones or phloroglucinol derivatives is extended to terpenoid-derived propargyl alcohols containing an internal alkyne moiety. A wide range of cyclic terpenoid and phloroglucinol adducts are obtained by complementary application of both types of catalysts.

Synthesis of Cyclopentenones with C4-Quaternary Stereocenters via Stereospecific [3,3]-Sigmatropic Rearrangement and Applications in Total Synthesis of Sesquiterpenoids

A cationic gold(I)-catalyzed asymmetric [3,3]-sigmatropic rearrangement of sulfonium leads after cyclization to cyclopentenones with a C4-quaternary stereocenter. Starting with simple vinyl sulfoxides and propargyl silane, numerous compounds were isolated with moderate to good yields and excellent enantiomeric excesses (26 examples). The application of this simple methodology allowed the efficient total synthesis of five natural sesquiterpenoids, including enokipodin A and B, hitoyopodin A, lagopodin A, and isocuparene-3,4-diol.

Recent Advances in Oxa-6π Electrocyclization Reactivity for the Synthesis of Privileged Natural Product Scaffolds

The stunning advances in understanding the reactivity and selectivity principles of asymmetric pericyclic reactions have had a profound impact on the synthetic planning of complex natural products. Indeed, electrocyclizations, cycloadditions, and sigmatropic rearrangements enable synthetic chemists to craft highly functionalized scaffolds that would not otherwise be possible with a similar atom-, step-, and redox-economy. In this review, selected examples from the last two decades of research (2003–2020) on tandem processes combining oxa-6π electrocyclic reactions are discussed in terms of reactivity challenges, inherent reversibility, and key structural bond formation in the assembly of natural products. A particular emphasis is given to the electrocyclic ring-closures in the tandem processes featuring Knoevenagel-type condensations, Diels–Alder cycloadditions, Stille couplings, and oxidative dearomatizations. The synthetic manifolds reviewed here illustrate how oxa-6π electrocyclizations are intimately linked to the construction of complex natural product scaffolds and have inspired a number of biomimetic syntheses in the laboratory.

Recent advances in catalytic asymmetric aza-Cope rearrangement

Aza-Cope rearrangement, as one of the fundamental reactions for C-C and C-N bond formation, has been extensively utilized for the rapid construction of synthetically challenging organic molecules. Despite significant achievements having been made in the past 80 years, catalytic enantioselective versions still remain a challenge, mainly due to the inherent nature of the reversibility of aza-Cope rearrangement. Recently, owing to the intensive development of asymmetric catalysis strategies, various chiral organocatalysts and transition-metal catalysts have been successfully applied to control the stereoselectivity of aza-Cope rearrangement, and remarkable advances have been achieved. This review highlights recent progress relating to catalytic asymmetric aza-Cope rearrangement and covers important features of these studies, including catalytic system design, mechanistic insights, stereochemistry analysis, and synthetic applications.

Melding of Experiment and Theory Illuminates Mechanisms of Metal-Catalyzed Rearrangements: Computational Approaches and Caveats

This review summarizes approaches and caveats in computational modeling of transition-metal-catalyzed sigmatropic rearrangements involving carbene transfer. We highlight contemporary examples of combined synthetic and theoretical investigations that showcase the synergy achievable by integrating experiment and theory.

1 Introduction

2 Mechanistic Models

3 Theoretical Approaches and Caveats

3.1 Recommended Computational Tools

3.2 Choice of Functional and Basis Set

3.3 Conformations and Ligand-Binding Modes

3.4 Solvation

4 Synergy of Experiment and Theory – Case Studies

4.1 Metal-Bound or Free Ylides?

4.2 Conformations and Ligand-Binding Modes of Paddlewheel Complexes

4.3 No Metal, Just Light

4.4 How To ‘Cope’ with Nonstatistical Dynamic Effects

5 Outlook

2-Indolymethanols as 4-atom-synthons in oxa-Michael reaction cascade: access to tetracyclic indoles

The first Brønsted acid-catalyzed oxa-Michael reaction cascade of 2-indolylmethanols with trione alkenes was accomplished. By using this practical approach, a variety of tetracyclic indoles were readily created in an ordered sequence with excellent regio- and diastereoselectivity. 2-Indolylmethanols commendably served as four-atom synthons, as opposed to the common three-atom synthons in the previous literature reports. The regioselectivity issue was well handled by the employment of a strong Brønsted acid catalyst. In addition, its dual role in activation of substrates via hydrogen-bonding interaction and acceleration of subsequent intramolecular cyclization and dehydration was proposed to account for the high reaction efficiency.

Borane-Catalyzed Carbazolation Reactions of Aryldiazoacetates

Herein, we report on the tris(pentafluorophenyl)borane-catalyzed reaction of carbazole heterocycles with aryldiazoacetates. We could demonstrate that selective N-H functionalization occurs in the case of an unprotected carbazole, other N-heterocycles, and secondary amines in good yields. In contract, the protected carbazole undergoes C-H functionalization at the C-3 position in a good yield. The application of both approaches was studied in 41 examples with up to a 97% yield.

Copper(II) Acetate-Induced Oxidation of Hydrazones to Diazo Compounds under Flow Conditions Followed by Dirhodium-Catalyzed Enantioselective Cyclopropanation Reactions

A tandem system comprising in-line diazo compound synthesis and downstream consumption in a rhodium-catalyzed cyclopropanation reaction has been developed. Passing hydrazone through a silica column absorbed with Cu(OAc)₂-H₂O/N,N-dimethylaminopyridine oxidized the hydrazone to generate an aryldiazoacetate in flow. The crude aryldiazoacetate elutes from this column directly into a downstream cyclopropanation reaction, catalyzed by the chiral dirhodium tetracarboxylates, Rh₂(R-p-Ph-TPCP)₄ and Rh₂(R-PTAD)₄. This convenient flow to batch method was applied to the synthesis of a range of 1,2-diarylcyclopropane-1-carboxylates in high yields and with high levels of enantioselectivity.

Enantioselective Photochemical Reactions Enabled by Triplet Energy Transfer

For molecules with a singlet ground state, the population of triplet states is mainly possible (a) by direct excitation and subsequent intersystem crossing or (b) by energy transfer from an appropriate sensitizer. The latter scenario enables a catalytic photochemical reaction in which the sensitizer adopts the role of a catalyst undergoing several cycles of photon absorption and subsequent energy transfer to the substrate. If the product molecule of a triplet-sensitized process is chiral, this process can proceed enantioselectively upon judicious choice of a chiral triplet sensitizer. An enantioselective reaction can also occur in a dual catalytic approach in which, apart from an achiral sensitizer, a second chiral catalyst activates the substrate toward sensitization. Although the idea of enantioselective photochemical reactions via triplet intermediates has been pursued for more than 50 years, notable selectivities exceeding 90% enantiomeric excess (ee) have only been realized in the past decade. This review attempts to provide a comprehensive survey on the various photochemical reactions which were rendered enantioselective by triplet sensitization.

Catalyst-Controlled Regiodivergence in Rearrangements of Indole-Based Onium Ylides

We have developed catalyst-controlled regiodivergent rearrangements of onium-ylides derived from indole substrates. Oxonium ylides formed in situ from substituted indoles selectively undergo [2,3]- and [1,2]-rearrangements in the presence of a rhodium and a copper catalyst, respectively. The combined experimental and density functional theory (DFT) computational studies indicate divergent mechanistic pathways involving a metal-free ylide in the rhodium catalyzed reaction favoring [2,3]-rearrangement, and a metal-coordinated ion-pair in the copper catalyzed [1,2]-rearrangement that recombines in the solvent-cage. The application of our methodology was demonstrated in the first total synthesis of the indole alkaloid (±)-sorazolon B, which enabled the stereochemical reassignment of the natural product. Further functional group transformations of the rearrangement products to generate valuable synthetic intermediates were also demonstrated.

Nitrone and Alkyne Cascade Reactions for Regio- and Diastereoselective 1-Pyrroline Synthesis

The synthesis of 1-pyrrolines from N-alkenylnitrones and alkynes has been explored as a retrosynthetic alternative to traditional approaches. These cascade reactions are formal [4+1] cycloadditions that proceed through a proposed dipolar cycloaddition and N-alkenylisoxazoline [3,3']-sigmatropic rearrangement. A variety of cyclic alkynes and terminal alkynes have been shown to undergo the transformation with N-alkenylnitrones under mild conditions to provide the corresponding spirocyclic and densely substituted 1-pyrrolines with high regio- and diastereoselectivity. Mechanistic studies provide insight into the balance of steric and electronic effects that promote the cascade process and control the diastereo- and regioisomeric preferences of the 1-pyrroline products. Diastereoselective derivatization of the 1-pyrrolines prepared by the cascade reaction demonstrate the divergent synthetic utility of the new method.

Reductive Arylation of Amides via a Nickel-Catalyzed Suzuki-Miyaura-Coupling and Transfer-Hydrogenation Cascade

We report a means to achieve the addition of two disparate nucleophiles to the amide carbonyl carbon in a single operational step. Our method takes advantage of non-precious-metal catalysis and allows for the facile conversion of amides to chiral alcohols via a one-pot Suzuki-Miyaura cross-coupling/transfer-hydrogenation process. This study is anticipated to promote the development of new transformations that allow for the conversion of carboxylic acid derivatives to functional groups bearing stereogenic centers via cascade processes.

Recent Perspectives on Rearrangement Reactions of Ylides via Carbene Transfer Reactions

Among the available methods to increase the molecular complexity, sigmatropic rearrangements occupy a distinct position in organic synthesis. Despite being known for over a century sigmatropic rearrangement reactions of ylides via carbene transfer reaction have only recently come of age. Most of the ylide mediated rearrangement processes involve rupture of a σ-bond and formation of a new bond between π-bond and negatively charged atom followed by simultaneous redistribution of π-electrons. This minireview describes the advances in this research area made in recent years, which now opens up metal-catalyzed enantioselective sigmatropic rearrangement reactions, metal-free photochemical rearrangement reactions and novel reaction pathways that can be accessed via ylide intermediates.

Rationalization of the mechanism and chemoselectivity of versatile Au-catalyzed reactions of diazoesters with allyl-functionalized sulfides, selenides, amines, or ethers by DFT

The origin of chemoselectivity and the mechanism of the title reactions were fully rationalized by density functional theory (DFT).