Synthesis of Eight‐Membered Lactams through Formal [6+2] Cyclization of Siloxy Alkynes and Vinylazetidines

Abstract

An ew approachf or the efficient synthesis of eightmembered lactams through formal [6+ +2] cyclization of siloxy alkynes and vinylazetidines has been developed. Evidence from ac hirality transfer experiment suggests that the reaction proceeds via a[3,3]-sigmatropic rearrangement from aketene intermediate.This insight led to the development of alternative conditions and use of acyl chlorides as ketene precursors for the [6+ +2] reaction with vinylazetidines.

Synthesis of Azocanes from Piperidines via an Azetidinium Intermediate

“…The access to medium‐size rings is challenging due to unfavorable enthalpic and entropic barriers and transannular interactions during the formation of these medium size rings [9,10] . The methods to access eight‐membered N‐heterocyclic systems are rare and most of the methods that have been developed are utilizing metals, such as transition metals which are expensive [11‐19] . Thus, free‐metal methods to access eight‐membered rings are attractive, [20–25] particularly rearrangements as these processes are atom economic and efficient and do not involve expensive and scarce metals.…”

Diastereoselective Access to Tetracyclic Eight‐Membered Lactams through a Dearomative Heck Reaction and an Alkylative Ring‐Opening Driven by Photoexcited Spiroindolines

“…[1] Owing to the unfavorable entropye ffects and transannular interactions, it is challengingt ob uild medium-sized rings directly from linear precursors. [2] Recent progress on medium-sized nitrogen heterocycles, whicha re versatile scaffolds found in biologically active natural products and pharmaceutically relevant compounds, engendered significant protocols based on pericyclic reactions, [3] cycloadditions [4] andr ing expansions. [5] Small carbo-and heterocycles such as cyclopropanes, cyclobutanones,a zetidines and oxetanes were employed as three-or four-membered components and the selective cleavage of CÀ Co rC ÀNb ond was performed.…”

Synthesis of Benzo[b]azocin‐2‐ones by Aryl Amination and Ring‐Expansion of α‐(Iodophenyl)‐β‐oxoesters

“…Very similar was the route published by Liu et al., who have replaced the PIFA‐oxidation step by photocatalysis with a Ru complex. A formal [6+2] cyclization of silyloxy alkynes and vinylazetidines leading to monocyclic azocanones was very recently reported by Wu et al …”

“…Aformal [6+ +2] cyclization of silyloxy alkynes and vinylazetidines leadingt om onocyclic azocanones was very recently reportedb yW uetal. [18] We have reported an access to eight-memberedr ing lactams by ring transformation of ten different b-oxoesters 5 with 1,4-dicarbonyl motif (Scheme 1). Bi-catalyzed conversion with 25 primary amines R 2 -NH 2 via azabicyclo[3.3.0]-intermediates 8 furnished alibrary of about250 hexahydroazocinones 9.…”