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

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 alpha,beta-unsaturated aldehydes with suitable substituted benzothiazinone derivatives. This process encompasses the initial formation of alpha,beta-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. image