Facile and Selective Synthesis of 4-Methyl- and 4-Phenylthiosemicarbazide (= N-Methyl- and N-Phenylhydrazinecarbothioamide) Derivatives of Benzil (= 1,2-Diphenylethane-1,2-dione)

摘要

A selective synthesis of 4-methylthiosemicarbazide (=N-methylhydrazinecarbothioamide; 4a) derivatives by reaction with benzil (= 1,2-diphenylethane-1,2-dione; 3) is described. The reaction conditions determined the condensation product formed. The most important factor was the acid used: in the presence of cone. HCl solution, the open-chain 2:1 compound la was exclusively obtained, whereas in the presence of 2m HCl, the cyclic 1:1 condensation product 2a was formed. The alcohol used, the presence of H2O, and the time of heating were additional crucial factors. The new cyclic compound 2a with a MeO group was exclusively formed when working under high-dilution conditions. The reaction with the 4-phenyl derivative 4b gave new cyclic compounds as the major products under all conditions used (Scheme).