Copper-Catalyzed Tandem Cross-Coupling/[2 + 2] Cycloaddition of 1,6-Allenynes with Diazo Compounds to 3-Azabicyclo[5.2.0] Ring Systems

Catalytic Schmittel-Type [2+2] Cycloaddition of γ-Alkynyl Diazoacetates with Terminal Alkynes for Accessing Cyclobuta[a]indenes

Instead of the conventional [4+2] cycloaddition, a regioselective Schmittel-type [2+2] cycloaddition of yne-allene esters, generated in situ from copper-catalyzed dediazotized coupling of γ-alkynyl diazoacetates with terminal alkynes, is reported, enabling a bicyclization process to produce a diverse array of C1-arylated cyclobuta[a]indenes in moderate to good yields. The protocol features wide functional group compatibility, mild reaction conditions, and experimental simplicity, holding significant potential for building new tricyclic cyclobutenes.

Enantioselective Synthesis of 1-Dihydrobenzazepines through Rh2(II)-Catalyzed Cycloisomerization of 1,6-Enyne

The 1-dihydrobenzazepine skeleton has emerged as a privileged structural motif in bioactive molecules. However, due to a lack of asymmetric methodology, access to chiral 1-dihydrobenzazepines has remained limited. Herein, we report the first intermolecular asymmetric cycloisomerization of benzo-fused enynes for the synthesis of chiral 1-dihydrobenzazepines via dirhodium catalysis. This methodology features high efficiency (up to 98% yield), high enantioselectivity (up to 99% ee), and broad scope of nucleophiles, including oxygen nucleophiles (alcohols, phenols, and carboxylic acids) and carbon nucleophiles (silyl enol ethers). Theoretical and experimental mechanistic studies reveal that the reaction pathway encompasses an asymmetric cycloisomerization, which gives rise to a dirhodium carbene containing a donor-acceptor (D-A) cyclopropane moiety, followed by a ring-opening process and stereoselective nucleophilic attack by external nucleophiles on the cyclopropyl ring. Control experiments demonstrate the pivotal role of the terminal group capped on the alkynyl group of substrates in achieving good efficiency.

Dodging the Conventional Reactivity of o-Alkynylanilines under Gold Catalysis for Distal 7-endo-dig Cyclization

A direct ring-closing strategy involving a less facile 7-endo-dig carbacyclization of o-alkynylaniline derivatives for the synthesis of benzo[b]azepines has been presented. The trivial well-documented 5-endo-dig cyclization in o-alkynylaniline derivatives due to high nucleophilicity of nitrogen has been overcome by using their vinylogous amides under gold catalysis to access a wide array of benzo[b]azepines in an atom economical way with excellent functional group compatibility. Deuterium scrambling experiments and DFT studies favor a mechanism involving stabilizing conformational change of the initially formed seven-membered vinyl gold intermediate through a key cyclopropyl gold carbene intermediate and its subsequent protodeauration mediated by the counter anion.

Unexpected Copper-Catalyzed Cascade Reaction of 1,6-Enynes with Sulfoxonium Ylides

An unprecedented copper-catalyzed cascade reaction of 1,6-enynes with sulfoxonium ylides is reported, providing a series of structurally intriguing 2,3-disubstituted indolines bearing a conjugated dienone functionality at the 3-position in moderate to excellent yields with good chemo-, regio-, and diastereoselectivities under mild reaction conditions. Importantly, sulfoxonium-ylide-derived copper-carbene herein exhibits quite different reactivity from that of diazo copper-carbene. A rational mechanism, an initial ammonium ylide rather than allene formation, is proposed.

Copper-Catalyzed Cycloadditions of Diazo Compounds with Imidazolidines/Hexahydropyrimidines for the Syntheses of N-Heterocycles

Reported herein are the unprecedented copper-catalyzed formal [n + 1]/[n + 3] (n = 5, 6) cycloadditions of diazo compounds with imidazolidines/hexahydropyrimidines, thus providing a general, economical, and efficient route to construct different sized (six- to nine-membered) diaza-heterocycles in moderate to excellent yields under mild reaction conditions. This strategy features the use of copper catalyst to accomplish such diverse annulations and the utilization of imidazolidines/hexahydropyrimidines as stable 1,5-/1,6-dipoles.

Enantioselective Synthesis of α-Aryl-β-Aminocyclopropane Carboxylic Acid Derivatives via Rh(II)-Catalyzed Cyclopropanation of Vinylsulfonamides with α-Aryldiazoesters

The reaction of vinylsulfonamides with donor-acceptor carbenes derived from α-aryldiazoesters, catalyzed by the tert-butyl glycine-derived dirhodium complex Rh₂(S-4-Br-NTTL)₄, has been reported. This method provides a variety of α-aryl-β-aminocyclopropane carboxylic acid derivatives bearing one quaternary carbon stereogenic center vicinal to the amino-substituted carbon in high yields with excellent diastereo- and enantioselectivities. Vinylsulfonamides showed complementary advantages over the well-developed vinylamides or vinylcarbamates for this Rh(II)-catalyzed cyclopropanation strategy. Moreover, these conformationally restricted α-aryl-β-aminocyclopropyl carboxylic acid derivatives can be readily incorporated into dipeptides.

Copper-Catalyzed Tandem Cross-Coupling/Thermally Promoted [2 + 2] Cycloaddition of 1,6-Enynes and Diazo Compounds To Assemble Methylenecyclobutane-Fused Ring System

An unprecedented copper-catalyzed tandem reaction of 1,6-enynes with diazo compounds via a cross-coupling/[2 + 2] cycloaddition sequence was reported. A library of methylenecyclobutane-fused ring systems including cyclobuta[b]indolines, cyclobuta[b]benzofuran, benzo[b]cyclobuta[d]thiophene, and bicyclo[3.2.0] structures were obtained in moderate to excellent yields under very mild reaction conditions. The reaction exhibited high proximal-regioselectivity and diastereoselectivity. Moreover, 1,6-allenene has proven to be the key intermediate and proceeds via a thermally promoted [2 + 2] cycloaddition in the absence of copper catalyst.

Recent Advances in the Tandem Cyclization/Cycloaddition of Allene Intermediates from Copper-Catalyzed Cross-Coupling of Diazo Compounds with Terminal Alkynes

This short review summarizes the most recent developments (since 2010) in the tandem cyclization/cycloaddition of allene intermediates­, generated from the copper-catalyzed cross-coupling of diazo compounds with terminal alkynes, to afford cyclic compounds.

1 Introduction

2 Cyclization

2.1 Cyclization with Nucleophiles

2.2 Cyclization with Electrophiles

2.3 6π-Electrocyclization

2.4 Other Cyclization

3 Cycloaddition

4 Conclusion

Copper-catalyzed cross-coupling and sequential allene-mediated cyclization for the synthesis of 1,2,3-triazolo[1,5-a]quinolines

In this paper, a tandem reaction involving copper-catalyzed cross-coupling and allene-mediated cyclization of 1-(2-ethynylaryl)-1,4-disubstituted-1,2,3-triazole with N-tosylhydrazone has been developed. This method features operational simplicity, excellent functional group compatibility, broad substrate scope, and easily available feedstock, providing an efficient and practical strategy for the synthesis of highly functionalized 1,2,3-triazolo[1,5-a]quinolines.