Copper-Catalyzed Geminal Difunctionalization of Terminal Alkynes by Splitting Sulfonyl Hydrazones into Two Parts

[4+1] Heteroannulation to Form 1-Pyrrolines through Alder-Ene Reaction of in situ Generated Ynimines: Development and Application in Total Synthesis of Borrecapine

We report in this paper a novel Cu-catalyzed synthesis of polysubstituted 1-pyrrolines. The reaction of β,γ-unsaturated oxime esters 4 with terminal alkynes 5 in the presence of a catalytic amount of Cu(OAc)2 and 2,2'-biquinoline affords the corresponding 1,6-enynimines, which undergo a highly stereoselective Alder-ene reaction to afford 1-pyrrolines with concomitant generation of a quaternary carbon and a 2-azadiene motif. It represents an unusual [4+1] heteroannulation reaction wherein terminal alkynes act as a one carbon donor and are 1,1-difunctionalized. Mechanistic studies suggest that the allylic hydrogen trans to the oxime ester main chain is selectively transferred to the electron-rich alkyne during the pericyclic reaction. The resulting 1-pyrrolines undergo facile acid-catalyzed regioselective Wagner-Meerwein rearrangement to provide 2H-pyrroles in excellent yields. The 2H-pyrroles are also accessible from 4 and 5 in a one-pot manner without isolation of the 1-pyrrolines. Leveraging this heteroannulation reaction as a key step, the first total synthesis of borrecapine, a 2,3,3,5-tetrasubstituted pyrrolidine, is accomplished.

Exploring the Divergent Reactivity of Vinyl Radicals Emanating from Alkynes and Thiols via Photoredox Catalysis

Organic chemistry has seen a surge in visible-light-driven transformations, which offer unique reaction pathways and access to new synthetic possibilities. We aim to provide a comprehensive understanding of state-of-the-art photo-mediated alkyne functionalization, with a focus on the reactive behavior of vinyl radicals. This review outlines our contributions to the field, including developing new methods for forming carbon-carbon and carbon-heteroatom bonds.

Copper iodide nanoparticles (CuI NPs): an efficient catalyst for the synthesis of alkynyl esters

An environmentally benign protocol for the synthesis of alkynyl esters, by the cross-coupling of diazoacetate with various substituted alkynes under neat reaction conditions, has been described. Copper iodide nanoparticles (CuI NPs) were found to promote the Sonogashira-type coupling to afford the corresponding alkynyl esters in good yields. The CuI nanoparticles were characterized by PXRD, FESEM, EDAX, and Raman techniques. The developed methodology has several advantages such as a broad substrate scope, less reaction time, atom economy, avoidance of an additive/base/solvent, and enhanced values of green chemistry. The catalyst was recycled up to threefold without the loss of its catalytic activity.

Recent Advances in Catalytic Alkyne Transformation via Copper Carbene Intermediates

As one of the abundant and inexpensive metals on the earth, copper has demonstrated broad applications in synthetic chemistry and catalysis. Among these copper-catalyzed advances, copper carbenes are versatile and reactive intermediates that can mediate a variety of transformations, which have attracted much attention in the past decades. The present review summarizes two different reaction models that take place between a copper carbene intermediate and alkyne species, including the cross-coupling reaction of copper carbene intermediate with terminal alkyne, and the addition of copper carbene intermediate onto the C-C triple bond. This article will cover the profile from 2010 to 2021 by placing emphasis on the detailed catalytic models and highlighting the synthetic applications offered by these practical and mild methods.

Atom-Economical, Catalyst-Free Hydrosulfonation of Densely Functionalized Alkenes: Access to Oxindole Containing Sulfones

An atom-economical hydrosulfonation of densely functionalized alkenes under catalyst-free conditions is described. Alkenes possessing hydroxy-oxindole moiety underwent hydrosulfonation on treatment with arylsulfinic acids in green media to afford the resulting...

Copper-Catalyzed 1,1-Alkylmonofluoroalkylation of Terminal Alkynes with Diazo Compounds and 2-Fluoro-1,3-dicarbonyl Compounds: Access toward (E)-β-Monofluoroalkyl-β,γ-unsaturated Esters or Ketones

An efficient copper-catalyzed three-component 1,1-alkylmonofluoroalkylation of terminal alkynes, diazo compounds, and 2-fluoro-1,3-dicarbonyl compounds for the synthesis of (E)-β-monofluoroalkyl-β,γ-unsaturated esters or ketones has been developed. The methodology features a broad substrate scope, an inexpensive and easily available catalytic system, and excellent selectivity with good yields. The mechanism of the tandem Cu-catalyzed cross-coupling and nucleophilic addition of allenes has been investigated.

Divergent functionalization of terminal alkynes enabled alkynylative [5+1] benzannulation of 3-acetoxy-1,4-enynes

We here describe an alkynylative [5+1] benzannulation of 3-acetoxy-1,4-enynes with terminal alkynes, which enables both the construction of a benzene ring skeleton and intermolecular incorporation of an alkynyl group in a single reaction using Pd and Cu cooperative catalysts. The method represents efficient access to internal aryl alkynes through divergent functionalization of two terminal alkyne components: one alkyne serves as the one-carbon unit to realize the [5+1] benzannulation and the other alkyne as a nucleophile terminates the reaction.

Visible-light-induced anti-Markovnikov hydrosulfonation of styrene derivatives

A visible-light-induced anti-Morkovnikov hydrosulfonation reaction of styrene derivatives with sodium sulfinates has been developed, featuring mild reaction conditions, good functional-group tolerance, good yields and high regioselectivity.

Synthetic and mechanistic aspects of sulfonyl migrations

Sulfonyl migrations, frequently described as ‘unusual’ or ‘unexpected’, from the last 20 years, including 1,2-, 1,3-, 1,4-, 1,5-, 1,6- and 1,7-sulfonyl shifts, through either radical or polar processes, either inter- or intramolecularly are reviewed.

Ligand-free copper-catalyzed regio- and stereoselective 1,1-alkylmonofluoroalkylation of terminal alkynes

A novel copper-catalyzed highly regio- and stereoselective 1,1-alkylmonofluoroalkylation of terminal alkynes without an external ligand has been developed.

Copper-catalyzed mild desulfonylation of vinyl sulfonyl molecules

The first Cu-catalyzed chemical selective desulfonylation of vinyl sulfonyl molecules to olefins was developed using B₂pin₂–water as the reductant.

Lewis Acid Catalyzed [4 + 2] Cycloaddition of N-Tosylhydrazones with ortho-Quinone Methides

A formal [4 + 2] cycloaddition of N-tosylhydrazones with ortho-quinone methides was developed, affording the facile synthesis of diverse 1,3-oxazine derivatives under mild conditions. In this transformation, N-tosylhydrazones are used as a 1,2-dipole synthon under base-free conditions. Moreover, the substrate scope is broad, and the products are formed with high diastereoselectivities in most of the cases.

Copper-catalyzed 1,1-arylalkylation of terminal alkynes with diazo esters and organoboronic acids

A novel copper-catalyzed 1,1-arylalkylation of terminal alkynes with diazo esters and organoboronic acids has been developed to construct (E)-β-aryl-β,γ-unsaturated esters.

Quick construction of a C–N bond from arylsulfonyl hydrazides and Csp2–X compounds promoted by DMAP at room temperature

A mild C–N coupling reaction with arylsulfonyl hydrazides and 2(5H)-furanones shows good yields, excellent reaction regioselectivity and functional group tolerance.