N‐Heterocyclic Carbene Organocatalyzed [3+3] Annulation for the Enantioselective Synthesis of Benzopyranothiazinones

Abstract

The design, inspired by the core‐structure of oxicam has allowed the enantioselective synthesis of benzopyranothiazinone motifs employing N‐heterocyclic carbene (NHC) catalysis. The NHC‐mediated transformation involves the reaction of α,β‐unsaturated aldehydes with suitable substituted benzothiazinone derivatives. This process encompasses the initial formation of α,β‐unsaturated acylazoliums from ynals and concurrent generation of enolates from benzothiazinone. The culmination of these reactions results in an efficient annulation, yielding the desired products with reasonable yields and high stereoselectivities. This study underscores the potential of NHC catalysis in the streamlined synthesis of complex heterocyclic structures.

Enantioselective synthesis of C3-functionalized 2,1-benzothiazine 2,2-dioxides by N-heterocyclic carbene catalysis

“…Recently, we demonstrated that the bioisosteric 1,2-benzothiazinone 1,1-dioxide system, in reaction with ynals, undergoes a stereoselective transformation into tricyclic benzopyrano-thiazinones with high enantioselectivity under NHC catalysis. 8…”