Exchange, elimination, and ring opening reactions of 2,3-dihydrobenzimidazo[1,2-d][1,2,4]thiadiazoles and 3H-benzimidazo[2,1-c][1,2,4]dithiazoles

Abstract

The reactions of benzimidazo[1,2-d][1,2,4]thiadiazol-3(2H)-ones (1) with isocyanates, isothiocyanates, carbon disulphide, aryl cyanates, acetylenedicarboxylates, and enamines, with exchange of the isocyanate component of (1), to give the corresponding condensed benzimidazole derivatives (1)–(6) are described. Under more severe conditions the 1-benzothiazol-2-yl-1,3-dihydrobenzimidazole-2-thiones (7) were obtained from aromatic isothiocyanates. Thermolysis of the thiadiazoles (1) led to the triazine derivative (12) with elimination of isocyanate and sulphur, and in the presence of phenols to the 2-aryloxybenzimidazoles (13). With amines and CH-acidic compounds, the S,N bond in compound (1) was cleaved to give benzimidazol-2-ylsulphenamides (14), and the ω-substituted methylthiobenzimidazoles (17) and (18). With cyanide ion, insertion into the S,N bond of compound (1) to furnish the thiadiazine (22) took place. The dithiazoles (2) were fragmented by amines to give 1,3-dihydrobenzimidazole-2-thione and guanidine with loss of sulphur; reaction with cyanide ion then gave the dibenzimidazothiadiazine (25).