Formal [3 + 4] Annulation of α,β-Unsaturated Acyl Azoliums: Access to Enantioenriched N-H-Free 1,5-Benzothiazepines.

An unprecedented formal [3 + 4] annulation of α,β-unsaturated acyl azoliums with 2-aminobenzenethiols has been utilized to synthesize enantioenriched N-H-free 1,5-benzothiazepines, which are recognized as privileged structures in numerous biologically active scaffolds. This protocol offers a rapid and direct pathway to access the target compounds with high enantioselectivities and has been applied in the concise synthesis of chiral drug (R)-thiazesim.