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 methyl tetrahydro-4-oxo-2H-thiopyran-3-carboxylate in refluxing 10% aqueous H 2 SO 4 . Reaction of tetrahydro-4H-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.Cyclic sulfides are an important class of compounds with numerous applications in many areas of chemistry. 1 In particular, thiopyran-derived scaffolds have been exploited in diverse ways. 2 The synthesis of such targets often involves the elaboration of simple thiopyran-containing reagents such as 2-4. 3 Of these, only tetrahydro-4H-thiopyran-4-one (3) is commercially available, albeit at a significant cost. 4 We have been investigating aldol reactions of 3 for the rapid assembly of stereochemically diverse polypropionate synthons and required large amounts of 2 and 3 for this purpose. 5 Herein we report simple and costefficient procedures for the preparation of 2, 3, and 4 (Scheme 1).Several methods for the synthesis of 3 are known, 3,6-9 most commonly by the decarboxylation of 2. 7-9 The bketo ester 2 is also a versatile reagent for synthesis of thiopyran-containing compounds and numerous reports on its preparation by Dieckmann cyclization of 1 10 or an analogous diester have been published. 7,8,11 Most of these methods involve the use of NaOMe or NaH in various modifications of Fehnel and Carmack's improvement of the original procedure by Bennet and Scorah. 7 Compared to the Fehnel and Carmack protocol (2 equiv of 'alcoholfree' NaOMe in refluxing diethyl ether; 64% yield of 2 on 1.4 mol scale), the modified procedures typically describe reactions on much smaller scale (<0.1 mol) and the reported yields vary widely (13-81%; most around 75%). The importance of the quality of the NaOMe used has been noted 9a and it is likely that the diester 1 is susceptible to hydrolysis by small amounts of NaOH. It is known that the reaction is accompanied by some cleavage of the sulfide linkage in 1, especially at higher temperatures, resulting in the formation of methyl 3-methoxypropionate, methyl 3-mercaptopropionate, and hydrogen sulfide. 9a Our experiments indicate that 2 readily decomposes under basic conditions in protic solution, perhaps contributing to the high variation in the reported yields.We previously reported a simplified procedure for the conversion of 1 into 2 (2 equiv of NaOMe in Et 2 O-THF; 93 ± 5% on 0.5 mol scale). 5b Subsequently, we optimized several reaction parameters and have now developed a very robust, scalable, and cost-effective procedure. The amount of NaOMe used can be reduced to 1.3 equivalents 12 and its quality is easily controlled with in situ generation by addition of anhydrous methanol to a suspension of Na metal in THF. Addition of 1 to the resulting NaOMe/THF mixture results in...