Thiadiazoles and thiadiazolines. Part 3. Synthesis of triazol-3-yl-Δ2-1,3,4-thiadiazolines and a new synthesis of unsymmetrical 2,5-di-substituted 1,3,4-thiadiazoles

Abstract

The reaction of 1-chloro-1,4-diphenyl-2,3-diazabutadiene (1) with 1-acetyl- and with 1-benzoyl-thiosemicarbazide yields initially the hydrochlorides of N²-acetyl- and N²-benzoyl-Δ²-1,3,4-thiadiazoline-4-carboxamide hydrazone (4a, b) which are converted by aqueous sodium hydroxide into the corresponding free bases (5a, b) and thence by cyclodehydration into 4-(4H-1,2,4-triazol-3-yl)-Δ²-1,3,4-thiadiazolines (6a, b). Treatment of (1) with thioacetamide, thionicotinamide, or the thiobenzamides 4-XC₆H₄CSNH₂(where X = H, MeO, and Cl), leads at 20–95 °C to 2-phenyl-5-R-1,3,4-thiadiazoles (9a–e)(where R = Me, 3-pyridyl, or 4-XC₆H₄). The reaction of (1) with guanidine leads, via the hydrochloride, to 3-amino-5-phenyl-4H-1,2,4-triazole. The mechanism of these and related reactions of (1) with other S-nucleophiles are discussed.