Regioselective Synthesis of Thiazole-5-thione Based on [2 + 3] Annulation Trapping of α-Keto Sulfine with Thioamide

Aiming to develop novel annulation reactions using sulfine intermediates, we have established a regioselective formal [2 + 3] cyclization reaction of α-keto sulfines generated from the elimination of arylacyl sulfoxides and thioamides. This new strategy allows for the synthesis of thiazole-5-thiones directly without catalysts or additives. The approach features a step-economic, one-pot characteristics via a tandem sequence of in situα-keto sulfines generation, regiospecifically nucleophilic attack or [3 + 2] cyclizatoin, dithioate (S=C−S−) skeletons formation, and subsequent intramolecular nucleophilic cyclization. This reaction also represents a novel method for constructing dithioate (S=C−S−) skeletons.