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-4H-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 metbyl tetrahydro-4-oxo-2H-thiopyran-3-carboxyl ate in refluxing 10% aqueous H2SO4. Reaction of tetrahydro-4H-thiopyran-4-one with Me3SiCI and Et3N in CHCl3 gave the corresponding trimethylsilyl enol ether in near quantitative yield. The prepared reagents are useful for the synthesis of thiopyran-containing compounds.