Studies of Acyl and Thioacyl Isocyanates. XIV. The Reactions of Benzoyl and Thiobenzoyl Isocyanates with Hydrazones

Abstract

Abstract Benzoyl (1) and thiobenzoyl isocyanates (2) reacted with benzaldehyde arylhydrazones and methylhydrazone to give the corresponding semicarbazones as isolated products respectively. In the reactions with acetone arylhydrazones and methylhydrazone, however, the s-triazolidin-5-ones whose structures corresponded to the ring tautomers of semicarbazones, were isolated as sole products from the reaction of 1, and 2 afforded the (4+2) cycloadducts of 2 to the C=N bond of hydrazones and s-triazolidin-5-ones. It has been found that in some cases, the semicarbazones isomerize into their ring tautomers, and the isomerization obeys good first-order kinetics taking into account the equilibrium. Although 1 did not react with p-tosyl- and benzoylhydrazones, 2 easily added to both hydrazones to yield the corresponding (4+2) cycloadducts.