Thiadiazoles and thiadiazolines. Part 2. Δ2-1,3,4-Thiadiazoline-4-carboxamidines derived from substituted acyclic thioureas

Abstract

A series of Δ²-1,3,4-thiadiazoline-4-carboxamidines (2b–f) and the corresponding amidinium chlorides have been prepared in 70–92% yield by reactions between 1-chloro-1,4-diphenyl-2,3-diazabutadiene (1) and the following thioureas: N-methylthiourea, N,N′-dimethylthiourea, N,N,N′-trimethylthiourea, N-allylthiourea, and N-phenylthiourea. Their spectroscopic properties are discussed, with particular reference to the amidine tautomerism. Attempts to achieve corresponding reactions between compound (1) and sterically hindered thioureas were unsuccessful. N,N′-Diphenylthiourea was converted into 3-anilino-4,5-diphenyl-4H-1,2,4-triazole (6), initially isolated as its hydrochloride; N,N′-di-t-butylthiourea gave 2,5-diphenyl-1,3,4-thiadiazole (8)(36%), the 4-(1-diazabutadienyl)-Δ²-1,3,4-thiadiazoline (9)(5%), di-t-butylurea (15%), and t-butylammonium chloride (6%). Mechanisms for these reactions are proposed.