Abstract
Reaction of 1,3-Thiazole-5(4H)-thiones and Diazomethane. Reaction of 4,4-dimethyl-1,3-thiazol-5(4H)-thiones1 with diazomethane in Et2O at -78° or 0° 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 of N2. Head-to-head dimerization of E yields 10, 1,3-dipolar cycloaddition of E and 1 gives the 'Schönberg 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° and at O° shows that, in contrast to the reaction of 1 and 2-diazopropane, the elimination of N2 in the primary cycloadduct already occurs at -78°.
Kägi, Martin