Synthesis of N ‐Heterocycles via [3 + n] Cycloaddition Reactions of Vinyl Metal Carbene Intermediates

Chiral Magnesium Complex-Catalyzed Asymmetric Cyclization of Vinyl Diazo Compounds with Phenol Derivatives via Noncarbene Pathways

“…As an important subclass, vinyl diazo compounds exhibit unique reactivities because of the extended alkene and intrigued broad interests from the chemistry community. Generally, more stabilized donor-/acceptor-substituted metal vinyl carbenoids can be formed by decomposition of the diazo group in the presence of transition-metal catalysts and thus mediate various transformations with regio- and stereoselectivity . In this regard, many asymmetric reactions have been reported (Scheme A top), such as cyclopropanation, cyclopropenation, [3 + 2] cycloaddition, tandem ylide formation/[2,3] sigmatropic rearrangements, C–H insertions, combined C–H activation/Cope rearrangement (CHCR), and X–H insertions .…”

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

“…Transition-metal-catalyzed reactions of diazo compounds have become a versatile tool in contemporary organic chemistry . Particularly, the transition-metal-catalyzed [ n + 1]/[ n + 3] cycloadditions of diazo compounds with 1, n -dipoles are powerful for the rapid construction of N-heterocycles, wherein the catalytically generated diazo metal-carbenes serve as reactive 1,1- or 1,3-dipolar species. , Albeit with impressive achievements, two major challenges still exist to improve the versatility of such cycloaddition strategy for N-heterocycle synthesis:…”

“…First, this field has been mainly dominated by rhodium catalysis. − In last decades, the copper-catalyzed reactions of diazo compounds have made distinct progress . In some cases, copper catalysts exhibit complementary ,− or even better catalytic performance than rhodium ones with remarkable levels of selectivities.…”

“…It is well-known that the metal-enolcarbenes exhibit carbenic and vinylogous reactivities. ,, In particular, metal-enolcarbenes are highly effective 1,3-dipolar adducts for [ n + 3] cycloadditions with 1, n -dipoles, wherein the nucleophilic addition occurs preferentially at the vinylogous position followed by subsequent intramolecular cyclization (Scheme , top). Therefore, we speculate that the [ n + 3] ( n = 5, 6) cycloadditions of metal-enolcarbenes with imidazolidines/hexahydropyrimidines could take place via a key zwitterionic iminium species IV and thus offer a concise approach to medium-sized (eight- and nine-membered) diaza-heterocycles (Scheme , bottom).…”