Simple and Efficient Preparation of Reagents for Thiopyran Introduction: Methyl Tetrahydro-4-oxo-2H-thiopyran-3-carboxylate, Tetrahydro-4H-thiopyran-4-one, and 3,6-Dihydro-4-trimethylsilyloxy-2H-thiopyran

Tetrahydro-4 H-thiopyran-4-one was prepared in >75% yield by treatment of dimethyl 3,3′-thiobispropanoate with NaOMe (generated in situ) in THF solution and decarboxylation of the resulting methyl tetrahydro-4-oxo-2 H-thiopyran-3-carboxylate in refluxing 10% aqueous H 2 SO 4 . Reaction of tetrahydro-4 H-thiopyran-4-one with Me 3 SiCl and Et 3 N in CHCl 3 gave the corresponding trimethylsilyl enol ether in near quantitative yield. The prepared reagents are useful for the synthesis of thiopyran-containing compounds.