N-Heterocyclic Carbene-Catalyzed in situ Activation of Alkynyl Acids for C-S Bond Formation: Access to Imidazo[2,1-b][1,3]thiazinones

Alkynyl acids are first utilized as alkynyl acylazolium precursors through an in situ activation strategy for the efficient construction of carbon-sulfur bond in a formal [3+3] annulation. This protocol offers a direct and rapid pathway for the synthesis of imidazo[2,1-b][1,3]thiazinone skeleton, a useful heterocyclic class frequently found in many bioactive compounds. This reaction also has the advantages of scalability, readily available materials, and simple manipulation in open air.