NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones

Org Lett. 2019 Nov 1;21(21):8598-8602. doi: 10.1021/acs.orglett.9b03188. Epub 2019 Oct 16.

Abstract

N-Heterocyclic carbene (NHC)-catalyzed [3 + 3] annulation of thioamides with modified enals allowing the enantioselective synthesis of functionalized 1,3-thiazin-4-ones is reported. The NHC generated from the chiral triazolium salt was optimal and the reaction is initiated by the thia-Michael addition to catalytically generated α,β-unsaturated acylazolium intermediates derived from 2-bromoenals, followed by intramolecular cyclization. This operationally simple procedure offers a straightforward and rapid access to target compounds in moderate to good yields and enantiomeric ratio values.