δ-Acetoxy Allenoate as a <i>5C</i>-Synthon in Domino-Annulation with Sulfamidate Imines: Ready Access to Coumarins

Abstract

A DMAP-catalyzed sequential benzannulation and lactonization strategy in which δ-acetoxy allenoate functions as a 5C-synthon in its reaction with cyclic sulfamidate imines is reported. This platform delivers π-extended coumarin frameworks under metal-free conditions via allylic elimination followed by Mannich coupling, proton shifts, C–N bond cleavage, and lactonization as key steps. The driving force for this domino reaction is the formation of the diene-ammonium intermediate and O–S bond cleavage. ESI-HRMS has been useful in gaining insights into the reaction pathway.