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.