First Isolation of Thione‐Propiolic Acid Adducts − Synthesis of Thiodioxenones

Abstract

Abstract Treatment of adamantane‐2‐thione ( 1a ) with propiolic acid ( 2a ) afforded a novel type of cycloadduct, spiro[adamantane‐2,2′‐[1,3]oxathiin]‐6‐one ( 3a ), in quantitative yield. The reaction proceeds through a concerted process, as was confirmed by kinetic analysis. Treatment of 1a with butynoic acid or phenylpropiolic acid gave the corresponding adducts regioselectively. Interestingly, only one isomer was obtained by treatment of thiofenchone with propiolic acid, suggesting that the reaction proceeded stereospecifically. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)