Synthesis of Enol Methyl Ethers of 3-Acetyl-6,6-dimethyltetrahydrothiopyran-2,4-dione and Their Reactions with Amines

The reaction of 3-acetyl-6,6-dimethyltetrahydrothiopyran-2,4-dione with diazomethane furnishes a mixture of 3-acetyl-6,6-dimethyl-4-methoxy-5,6-dihydro-2H-thiopyran-2-one and 3-acetyl-6,6-dimethyl- 2-methoxy-5,6-dihydro-2H-thiopyran-4-one in 2:3 ratio, whereas in reaction with dimethyl sulfate in the presence of potassium carbonate forms a mixture of the same products in 9:1 ratio. In both reactions the overall yield of ethers amounts to 50%. Treating of regioisomeric enol methyl ethers with pyrrolidine, o-toluidine, and allylamine provides the corresponding endocyclic enaminodiketones.