Reactions of α,β-unsaturated thioamides with diazo compounds

Several reactions of the alpha,beta-unsaturated thioamide 8 with diazo compounds 1a-1d were investigated. The reactions with CH2N2 (1a), diazocyclohexane (1b), and phenyldiazomethane (1c) proceeded via a 1,3-dipolar cycloaddition of the diazo dipole at the C=C bond to give the corresponding 4,5-dihydro-1H-pyrazole-3-carbothioamides 12a-12c, i.e., the regioisomer which arose from the bond formation between the N-terminus of the diazo compound and the C(alpha)-atom of 8. In the reaction of la with 8, the initially formed cycloadduct, the 4,5-dihydro-3H-pyrazole-3-carbothioamide 11a, was obtained after a short reaction time. In the case of 1c, two tautomers 12c and 12c' were formed, which, by derivatization with 2-chlorobenzoyl chloride 14, led to the crystalline products 15 and 15'. Their structures were established by X-ray crystallography. From the reaction of 8 and ethyl diazoacetate (1d), the opposite regioisomer 13 was formed. The monosubstituted thioamide 16 reacted with la to give the unstable 4,5-dihydro-1H-pyrazole-3-carbothioamide 17.