Reaction of 1,3-Thiazole-5(4H)-thiones with Diazomethane

Article abstract of DOI:10.1002/hlca.19930760428

Reaction of 4,4-dimethyl-1,3-thiazol-5(4H)-thiones 1 with diazomethane in Et2O at -78 deg C or 0 deg C leads to a mixture of the corresponding 1,4-dithiane 10, 1,3-dithiole 11, thiirane 12, 4,5-dihydro-5-methylidene-1,3-thiazole 13, and 1,3-thiazol-5(4H)-one 14 (Scheme 3).The structures of 10a, 11a, and 11b have been established by X-ray crystallography.The formation of the products can be explained via an intermediate thiocarbonyl ylide of type E (Scheme 4), generated by the 1,3-dipolar cycloaddition of diazomethane with the exocyclic C=S bond of 1 and elimination ofN2.Head-to-head dimerization of E yields 10, 1,3-dipolar cycloaddition of E and 1 gives the Schoenberg product 11, and cyclization of E leads to 12, which undergoes a desulfurization to give 13.The thiazolone 14 is formed by hydrolysis of E.The similarity of the ratio of the products at -78 deg C and at 0 deg C shows that, in contrast to the reaction of 1 with 2-diazopropane, the elimination of N2 in the primary cycloadduct already occurs at -78 deg C.