Asymmetric Catalytic (2+1) Cycloaddition of Thioketones to Synthesize Tetrasubstituted Thiiranes

Abstract

Herein, we report the first example of enantioselective (2+1) cycloaddition of thioketones with α‐diazo pyrazoleamides for the direct synthesis of tetrasubstituted thiiranes. In the presence of chiral N,N′‐dioxide/cobalt(ΙΙ) complexes (2–5 mol%), excellent efficiency (up to 99 % yield within 15 mins) and high stereoselectivity (up to >19 : 1 dr and 97 % ee) are available. Elaborations of thiiranes via desulfuration have also been conducted to deliver tetrasubstituted olefins. Density functional theory calculations reveal that the reaction initiates from a doublet state cobalt(ΙΙ) carbenoid, which is followed by a quartet cobalt(ΙΙ)‐bound thiocarbonyl ylide pathway. This work provides a route for the selective construction of tetrasubstituted thiiranes and olefins that are otherwise difficult to access.

Synthesis of cis-thiiranes as diastereoselective access to epoxide congeners via 4π-electrocyclization of thiocarbonyl ylides

“…Alternatively, the episulfidation of alkenes has been investigated 15 , but this seemingly straightforward epoxidation-like approach is applicable only to a limited range of cyclic alkenes. Otherwise, stereoselective synthesis of thiiranes has rarely been developed [41][42][43][44][45] , and most of the reported examples have serious drawbacks such as low stereoselectivity, narrow substrate scope, and/ or the requirement of highly toxic reagents. Among these precedents, a unique synthetic sequence of the Barton-Kellogg reaction is noteworthy (Fig.…”