A Direct Synthesis of Allenes by a Traceless Petasis Reaction

Recent Trends in the Petasis Reaction: A Review of Novel Catalytic Synthetic Approaches with Applications of the Petasis Reaction

The Petasis reaction, also called the Petasis Borono-Mannich reaction, is a multicomponent reaction that couples a carbonyl derivative, an amine and boronic acids to yield substituted amines. The reaction proceeds efficiently in the presence or absence of a specific catalyst and solvent. By employing this reaction, a diverse range of chiral derivatives can easily be obtained, including α-amino acids. A broad substrate scope, high yields, distinct functional group tolerance and the availability of diverse catalytic systems constitute key features of this reaction. In this review article, attention has been drawn toward the recently reported methodologies for executing the Petasis reaction to produce structurally simple to complex aryl/allyl amino scaffolds.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

Visible-Light Photoredox Catalyzed Regioselective 1,4-Hydroalkylation of 1,3-Enyne

Described herein is a visible-light photoredox-catalyzed regioselective 1,4-hydroalkylation of 1,3-enynes. Various of di- and tri-substituent allenes were really accessible under the present reaction conditions. The visible-light photoredox activation of the carbon nucleophile to generate its radical species, allowing the addition with un-activated enynes. The synthetic utility for the present protocol was demonstrated by a large-scale reaction, as well as the derivatization of the allene product.

Synthesis of α-allenic aldehydes/ketones from homopropargylic alcohols using a visible-light irradiation system

A visible-light irradiation tandem oxidative aryl migration/carbonyl formation reaction, mediated by K₂S₂O₈ and visible-light photoredox catalysis, has been discovered. The presented transformation provides a straightforward access to important α-allenic aldehyde/ketone derivatives from readily available homopropargylic alcohol derivatives in a regioselective manner of 1,4-aryl shift concomitant with carbonyl formation. The operational simplicity and broad substrate scope demonstrate the great potential of this method for the synthesis of highly functional α-allenic aldehyde/ketone derivatives.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

ASYMMETRIC SYNTHESIS: A GLANCE AT VARIOUS METHODOLOGIES FOR DIFFERENT FRAMEWORKS

Abstract:

Asymmetric reactions have made a significant advancement over the past few decades and involved the production of enantiomerically pure molecules using enantioselective organocatalysis, chiral auxiliaries/substrates, and reagents via controlling the absolute stereochemistry. The laboratory synthesis from an enantiomerically impure starting material gives a combination of enantiomers which are difficult to separate for chemists in the fields of medicine, chromatography, pharmacology, asymmetric synthesis, studies of structure-function relationships of proteins, life sciences and mechanistic studies. This challenging step of separation can be avoided by the use of asymmetric synthesis. Using pharmacologically relevant scaffolds/pharmacophores, the drug designing can also be achieved using asymmetric synthesis to synthesize receptor specific pharmacologically active chiral molecules. This approach can be used to synthesize asymmetric molecules from wide variety of reactants using specific asymmetric conditions which is also beneficial for environment due to less usage and discharge of chemicals into the environment. So, in this review, we have focused on the inclusive collation of diverse mechanisms in this area, to encourage auxiliary studies of asymmetric reactions to develop selective, efficient, environment-friendly and high yielding advanced processes in asymmetric reactions.

Direct and Efficient Synthesis of Tetrasubstituted Allenyl organothiophosphates from Propargylic Alcohols under Catalyst- and Additive-Free Conditions

An environment-friendly approach that affords tetrasubstituted allenyl organothiophosphates containing highly congested carbon centers from easily prepared propargylic alcohols and phosphorothioic acids [(RO)2P(O)SH] with water as the only by-product is developed....

Divergent, C-C Bond Forming Macrocyclizations Using Modular Sulfonylhydrazone and Derived Substrates

A divergent approach to C-C bond forming macrocycle construction is described. Modular sulfonylhydrazone and derived pyridotriazole substrates with three key building blocks have been constructed and cyclized to afford diverse macrocyclic frameworks. Broad substrate scope and functional group tolerance have been demonstrated. In addition, site-selective postfunctionalization allowed for further diversification of macrocyclic cores.

EATA Reaction Catalyzed by Copper Halides of Mixed Oxidation States and Its Application to Total Synthesis of Scorodonin

Naturally occurring conjugated allenynes are of general interest to the scientific community for their potent and various biological activities. The 1,5-H transfer of alka-1,4-diyn-3-yl amines would be one of the most straightforward yet challenging approach to this class of compounds since it may, in principle, form two regioisomeric products involving two different C-C triple bonds. Herein, a catalytic recipe of copper halides with mixed oxidation states, i.e., CuCl/CuBr 2 , has been identified to address the issues of the side reaction of conjugate addition and the selectivity of 1,5-H transfer of the key intermediate, alka-1,4-diyn-3-yl amines, in EATA (Enantioselective Allenation of Terminal Alkynes) reaction involving the conjugated 2-alkynals. This protocol could accommodate a wide range of functional groups providing a series of allenynes with a very high enantioselectivity (up to >99% ee). In addition, the enantioenriched allenynes can be readily transformed into various building blocks and applied to the highly enantioselective total synthesis of linear allenic natural product scorodonin for the first time. Mechanistic studies and DFT calculations elucidated the high regioselectivity for observed 1,5-H transfer within the intermediate of 1,4-diyn-3-yl amines. The calculated energy difference between two of the most stable transition states of 3.4 kcal/mol accounts for a selectivity of over 99:1, which is in perfect agreement with the experimental results.

Regioselective Cross-Coupling of Isatogens with Boronic Acids to Construct 2,2-Disubstituted Indolin-3-one Derivatives

Herein we present a transition-metal-free cross-coupling reaction of isatogens with boronic acids through a 1,4-metalate shift of a boron "ate" complex. This coupling reaction provides a feasible method to deliver valuable 2,2-disubstituted indolin-3-one derivatives with excellent regioselectivity, which exhibit operational simplicity, good functional group tolerance, and a broad substrate scope.

Zinc Iodide Catalyzed Synthesis of Trisubstituted Allenes from Terminal Alkynes and Ketones

A straightforward, user-friendly, efficient protocol for the one pot, ZnI₂-catalyzed allenylation of terminal alkynes with pyrrolidine and ketones, toward trisubstituted allenes, is described. Trisubstituted allenes can be obtained under either conventional heating or microwave irradiation conditions, which significantly reduces the reaction time. A sustainable, widely available, and low-cost metal salt catalyst is employed, and the reactions are carried out under solvent-free conditions. Among others, synthetically valuable allenes bearing functionalities such as amide, hydroxyl, or phthalimide can be efficiently prepared. Mechanistic experiments, including kinetic isotope effect measurements and density functional theory (DFT) calculations, suggest a rate-determining [1,5]-hydride transfer during the transformation of the intermediate propargylamine to the final allene.

Tetracoordinate Boron Intermediates Enable Unconventional Transformations

ConspectusOrganoboron compounds are a class of multifunctional reagents for the construction of carbon-carbon and carbon-heteroatom bonds in modern synthetic chemistry. The transformations of organoboron compounds are usually carried out through tetracoordinate boron intermediates and mainly include additions to unsaturated bonds, rearrangement reactions, transmetalation reactions, and so on. Although great progress has been achieved in improving tetracoordinate boron intermediates, there are still shortcomings, such as sparse activation modes, a paucity of reaction strategies and difficulties in stereoselective control. In this Account, we mainly discuss our recent advances in the development of unconventional transformations of organoboron compounds based on the design of tetracoordinate boron intermediates, including the following three topics: (1) the construction of C-B bonds; (2) the construction of C-C bonds; (3) the design and application of chiral tetracoordinate boron.The development of new strategies to build C-B bonds is of great interest for chemists. We have developed tandem reactions involving multiple tetracoordinate boron intermediates for the selective borylations of alkynes and the synthesis of stable tetracoordinate boron, including a domino-borylation-protodeboronation (DBP) strategy for selective borylations of alkynes, highly regio-, stereo-, and chemoselective Cu-catalyzed diborylation of β-CF₃-1,3-enynes and cascade B-Cl/C-B cross-metathesis and C-H bond borylation for the synthesis of tetracoordinate triarylboranes. We have also developed novel strategies involving tetracoordinate boron intermediates to form C-C bonds because the formation of C-C bonds is an enduring theme of organic chemistry. We disclosed long distance or multiple migration reactions and novel coupling partners in transmetalation reactions, such as long distance 1,4-migrations of tetracoordinate nitrile oxide boron and nitrilium boron intermediates, multiple migrations of tetracoordinate isocyanide boron intermediate, palladium-catalyzed Suzuki-Miyaura coupling of thioureas or thioamides, copper-catalyzed atroposelective Michael-type addition, and a palladium-catalyzed atroposelective Catellani reaction. Moreover, in terms of stereoselective control of the tetracoordinate boron intermediate, we found that a chiral tricoordinate boron complex could activate water to form a chiral tetracoordinate boron complex with Brønsted acidity, which has been successfully applied with high enantioselectivity to the asymmetric catalytic reduction of challenging indoles.This Account summarizes our recent efforts using unconventional transformations of organoboron compounds for the design of tetracoordinate boron intermediates, which not only achieved the precise construction of a wide range of diverse C-B bonds and C-C bonds but also developed a novel chiral Brønsted acid for the asymmetric catalytic reduction of challenging indoles.

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.

Passerini-type reaction of boronic acids enables α-hydroxyketones synthesis

Multicomponent reactions (MCRs) facilitate the rapid and diverse construction of molecular scaffolds with modularity and step economy. In this work, engagement of boronic acids as carbon nucleophiles culminates in a Passerini-type three-component coupling reaction towards the synthesis of an expanded inventory of α-hydroxyketones with skeletal diversity. In addition to the appealing features of MCRs, this protocol portrays good functional group tolerance, broad substrate scope under mild conditions and operational simplicity. The utility of this chemistry is further demonstrated by amenable modifications of bioactive products and pharmaceuticals as well as in the functionalization of products to useful compounds.

Multicomponent reactions enable the rapid construction of diverse molecular scaffolds with modularity and step economy. In this work, the authors report the use of boronic acids as carbon nucleophiles in a Passerini-type three-component coupling reaction towards an expanded inventory of α-hydroxyketones.

Organocatalytic Enantioselective Conjugate Alkynylation of β-Aminoenones: Access to Chiral β-Alkynyl-β-Amino Carbonyl Derivatives

Readily available potassium alkynyltrifluoroborates were used for organocatalytic asymmetric conjugate alkynylation of β-enaminones. The interception of a modified binaphthol catalyst and in situ generated organodifluoroboranes proved important to access functionalized β-alkynyl-β-amino carbonyls and derivatives with improved chemo-reactivity and enantio-induction. Mechanistic studies revealed the impact of molecular sieves on efficiency and stereocontrol. The products undergo additional functionalization to yield a diverse set of valuable β-alkynyl-β-amino carbonyl scaffolds.

Oxidation of Alkynyl Boronates to Carboxylic Acids, Esters, and Amides

A general efficient protocol was developed for the synthesis of carboxylic acids, esters, and amides through oxidation of alkynyl boronates, generated directly from terminal alkynes. This protocol represents the first example of C(sp)-B bond oxidation. This approach displays a broad substrate scope, including aryl and alkyl alkynes, and exhibits excellent functional group tolerance. Water, primary and secondary alcohols, and amines are suitable nucleophiles for this transformation. Notably, amino acids and peptides can be used as nucleophiles, providing an efficient method for the synthesis and modification of peptides. The practicability of this methodology was further highlighted by the preparation of pharmaceutical molecules.

Catalyst-Free One-Pot Synthesis of Densely Substituted Pyrazole-Pyrazines as Anti-Colorectal Cancer Agents

The first catalyst-free post-Ugi cascade methodology was developed for expeditious access to structurally diverse and complex pyrazole-pyrazines in one-pot. This novel cascade reaction features an intramolecular N2-arylation of pyrazoles with allenes at the C-β position of triple bond. Screening in the colorectal cancer cell lines HCT116 and SW620 validated the feasibility of the methodology for generating bioactive compounds. The lead compound 7h which is active against HCT116 and SW620 with IC₅₀ of 1.3 and 1.8 µM, respectively, can be synthesized and purified in a gram process synthetic scale in 7 hours. The mechanical studies indicated that compound 7h can induce cell cycle arrest in the G2/M phase and inhibit proliferation and viability in human colon cancer cells. Overall, compound 7h is represented as a promising starting point for the development of new anti-colorectal cancer drugs.

Cu-Catalyzed Synthesis of Tetrasubstituted 2,3-Allenols through Decarboxylative Silylation of Alkyne-Substituted Cyclic Carbonates

An efficient and mild Cu-catalyzed protocol has been developed for the decarboxylative silylation of alkyne-functionalized cyclic carbonate substrates affording 2,3-allenols featuring four different substituents. This practical methodology gives access to a wide scope of tetrasubstituted functionalized allenes in excellent yields.

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

The Petasis boron-Mannich reaction, simply referred to as the Petasis reaction, is a powerful multicomponent coupling reaction of a boronic acid, an amine, and a carbonyl derivative. Highly functionalized amines with multiple stereogenic centers can be efficiently accessed via the Petasis reaction with high levels of both diastereoselectivity and enantioselectivity. By drawing attention to examples reported in the past 8 years, this Review demonstrates the breadth of the reactivity and synthetic applications of Petasis reactions in several frontiers: the expansion of the substrate scope in the classic three-component process; nonclassic Petasis reactions with additional components; Petasis-type reactions with noncanonical substrates, mechanism, and products; new asymmetric versions assisted by chiral catalysts; combinations with a secondary or tertiary transformation in a cascade- or sequence-specific manner to access structurally complex, natural-product-like heterocycles; and the synthesis of polyhydroxy alkaloids and biologically interesting molecules.

Copper-catalyzed 1,4-alkylarylation of 1,3-enynes with masked alkyl electrophiles

Classical 1,4-dicarbofunctionalization of 1,3-enynes employs organometallic reagents as nucleophiles to initiate the reaction. We report a copper-catalyzed 1,4-alkylarylation of 1,3-enynes with alkyl diacyl peroxides as masked alkyl electrophiles and aryl boronic acids as nucleophiles, selectively affording structurally diversified tetrasubstituted allenes under mild conditions. Mechanistic studies suggest that an allenyl radical might be involved.

Copper-Catalyzed Radical 1,4-Difunctionalization of 1,3-Enynes with Alkyl Diacyl Peroxides and N-Fluorobenzenesulfonimide

Many reactions involving allenyl ion species have been studied, but reactions involving allenyl radicals are less well understood, perhaps because of the inconvenience associated with the generation of short-lived allenyl radicals. We describe here a versatile method for the generation of allenyl radicals and their previously unreported applications in the intermolecular 1,4-carbocyanation and 1,4-sulfimidocyanation of 1,3-enynes. With the assistance of the trifunctional reagents, alkyl diacyl peroxides or N-fluorobenzenesulfonimide, a range of synthetically challenging multisubstituted allenes can be prepared with high regioselectivity. These multisubstituted allenes can be easily transformed into synthetically useful structures such as fluorinated vinyl cyanides, lactones, functionalized allenyl amides, 1-aminonaphthalenes, and pyridin-2(1 H)-ones, and several novel transformations are reported. The results of radical scavenger and radical clock experiments are consistent with the proposed allenyl radical pathway. Density functional theory (DFT) and IR spectroscopy studies suggest the formation of an isocyanocopper(II) species in the ligand exchange step. On the basis of the results of IR, DFT, and diastereoselectivity studies, an isocyanocopper(II)/copper(I) catalytic cycle is proposed, which differs from the previously considered Cu(III) mechanism in cyanation reactions.

Chiral Diol-Based Organocatalysts in Enantioselective Reactions

Organocatalysis has emerged as a powerful synthetic tool in organic chemistry in the last few decades. Among various classes of organocatalysis, chiral diol-based scaffolds, such as BINOLs, VANOLs, and tartaric acid derivatives, have been widely used to induce enantioselectivity due to the ability of the hydroxyls to coordinate with the Lewis acidic sites of reagents or substrates and create a chiral environment for the transformation. In this review, we will discuss the applications of these diol-based catalysts in different types of reactions, including the scopes of reactions and the modes of catalyst activation. In general, the axially chiral aryl diol BINOL and VANOL derivatives serve as the most competent catalyst for most examples, but examples of exclusive success using other scaffolds, herein, suggests that they should not be overlooked. Lastly, the examples, to date, are mainly from tartrate and biaryl diol catalysts, suggesting that innovation may be available from new diol scaffolds.

Petasis three-component reactions for the synthesis of diverse heterocyclic scaffolds

The Petasis three-component reaction (PR) of hydroxy aldehydes, amines and boronic acids is an important multi-component reaction for the synthesis of structurally diverse scaffolds and biologically interesting small molecules. The reaction has been significantly explored in the past decade, and many new variants have emerged, such as asymmetric, traceless and four-component approaches. The excellent stereoselectivity, high yield and broad functional group tolerance altogether make this reaction ideal for fragment and compound collection synthesis, since orthogonal chemical handles can be incorporated for subsequent scaffold formation and appendage modification. Herein we present a selection of recent variations on the PR theme for the synthesis of scaffolds of relevance to medicinal chemistry.

Functionalized Spiroindolines with Anticancer Activity through a Metal-Free Post-Ugi Diastereoselective One-Pot Cascade Reaction

A post-Ugi diastereoselective one-pot cascade reaction requiring no metal catalyst was developed. The reaction scope was wide with mild conditions and good yields. A collection of spiroindolines was prepared by the protocol and screening tests in several difficult-to-inhibit cancer cell lines were conducted. The relationship of structure and anticancer activities was promising and in the Huh7 cell lines compound 16 j is more potent than Vinbalstine. The cyclization design strategy could be applicable to other multicomponent reactions (MCRs) for synthesizing bioactive and drug-like heterocycles.

The acid promoted Petasis reaction of organotrifluoroborates with imines and enamines

The acid promoted addition of organotrifluoroborate salts to imine and enamine electrophiles is reported. Use of the pre-activated trifluoroboronate complex bypasses the need for α-hetero substitution on the electrophile component, greatly expanding the scope of the Petasis borono-Mannich reaction. A variety of vinyl, aromatic and heteroaromatic trifluoroborate salts undergo addition with good efficiency under mild reaction conditions. The reaction is amenable for use with a variety of carbamate protected imine and enamine electrophiles, achieving for the first time the effective coupling with aliphatic aldehydes.

Enantioselective Synthesis of β-Allenoates via Phosphine-Catalyzed and ZnI2-Promoted Preparation of Oxazolidines and Propargylamines Using Chiral Amines, 1-Alkynes, and Propiolates

Diphenylphosphinoethane (DPPE)-catalyzed and ZnI₂-promoted in situ formation of oxazolidine, alkynyl zinc, and propargylamine intermediates from 1-alkynes, chiral (S)-diphenyl(pyrrolidin-2-yl)methanol, and propiolates gave the corresponding chiral (R)-β-allenoates in 40-72% yield with up to >99% ee. The intermediate propargylamine was isolated in 50% yield and converted to give the β-allenoate 10aa in 68% yield and 96% ee upon reaction with ZnI₂. The results are discussed considering a mechanism involving oxazolidine and iminium ions formed in situ followed by addition of alkynyl zinc complex to produce the propargylamine that gives the corresponding allenoate via a 1,5-hydrogen shift in the presence of ZnI₂.

Asymmetric Traceless Petasis Borono-Mannich Reactions of Enals: Reductive Transposition of Allylic Diazenes

The traceless Petasis borono-Mannich reaction of enals, sulfonylhydrazines, and allylboronates, catalyzed by chiral biphenols, results in an asymmetric reductive transposition of the in situ generated allylic diazene. Acyclic 1,4-diene products bearing either alkyl- or aryl-substituted benzylic stereocenters are afforded in excellent yields and enantiomeric ratios of up to 99:1. The use of crotylboronates in the reaction results in concomitant formation of two stereocenters in either a 1,4-syn or anti relationship from the corresponding E- or Z-crotylboronate used in the reaction. The use of β-monosubstituted enals in the asymmetric traceless Petasis borono-Mannich reaction of crotylboronates installs tertiary methyl-bearing stereocenters in good yields and high enantioselectivities.

Carbon-Nitrogen Bond Formation via the Vanadium Oxo Catalyzed Sigmatropic Functionalization of Allenols

A vanadium catalyzed 1,3-rearrangement of allenols to form transient vanadium enolates that selectively couple with electrophilic nitrogen sources is reported even in the presence of competing simple protonation and Alder-ene pathways. Hydrazine products can be cyclized in a 6-endo-trig fashion which, upon reductive cleavage of the N-N bond, yield 1,4-diamines. Additionally, cleavage of the N-N bond before cyclization can be achieved to form β-hydroxy amines, a common structural motif of biologically active compounds.

Enantioselective Synthesis of Allenes by Catalytic Traceless Petasis Reactions

Allenes are useful functional groups in synthesis as a result of their inherent chemical properties and established reactivity patterns. One property of chemical bonding renders 1,3-substituted allenes chiral, making them attractive targets for asymmetric synthesis. While there are many enantioselective methods to synthesize chiral allenes from chiral starting materials, fewer methods exist to directly synthesize enantioenriched chiral allenes from achiral precursors. We report here an asymmetric boronate addition to sulfonyl hydrazones catalyzed by chiral biphenols to access enantioenriched allenes in a traceless Petasis reaction. The resulting Mannich product from nucleophilic addition eliminates sulfinic acid, yielding a propargylic diazene that performs an alkyne walk to afford the allene. Two enantioselective approaches have been developed; alkynyl boronates add to glycolaldehyde imine to afford allylic hydroxyl allenes, and allyl boronates add to alkynyl imines to form 1,3-alkenyl allenes. In both cases, the products are obtained in high yields and enantioselectivities.

Silver-Catalyzed [2+1] Cyclopropenation of Alkynes with Unstable Diazoalkanes: N-Nosylhydrazones as Room-Temperature Decomposable Diazo Surrogates

The [2+1] cycloaddition of alkynes with diazo compounds represents one of the most powerful and reliable methods for the construction of cyclopropenes. However, it remains a formidable challenge to accomplish the cyclopropenation of alkynes with non-stabilized diazoalkanes, owing to the fact that such compounds are unstable and prone to detonation. Herein, we report a general silver-catalyzed cyclopropenation reaction of alkynes with unstable diazoalkanes, by for the first time the discovery and application of N-nosylhydrazones as room-temperature decomposiable diazo surrogates. This method allows for the efficient assembly a wide variety of cyclopropene derivatives that are otherwise difficult to access by conventional methods.

Recent advances in catalytic asymmetric synthesis of allenes

This minireview summarizes the recent advances in the synthesis of allenes with catalytic asymmetric methods.

Short synthesis of polyfunctional sp3-rich threonine-derived morpholine scaffolds

A convenient synthesis of sp³-rich complex morpholines was achieved in two steps involving a Petasis three-component coupling reaction followed by an acid- or base-mediated cyclization.

Copper-catalyzed silylation reactions of propargyl epoxides: easy access to 2,3-allenols and stereodefined alkenes

Efficient silylation reactions of propargyl epoxides catalyzed by copper catalysts have been developed.