Azodicarboxylates: valuable reagents for the multicomponent synthesis of novel 1,3,4-thiadiazoles and imidazo[2,1-b][1,3,4]thiadiazoles

Upon reaction of 4,5-disubstituted-N-arylaminoimidazole-2-thiones with isocyanides in the presence of azodicarboxylates (1.2 equiv) at rt, the imidazo[2,1-b][1,3,4]thiadiazoles were formed as the only reaction products in very good yields, whereas by using higher reaction temperatures, along with the imidazo[2,1-b][1,3,4]thiadiazoles, the three component reaction products, namely thiadiazoles, were also isolated, their formation being dependent on the 5-thione substituent. The thiadiazoles became the only reaction products, formed in very good yield by using 2 equiv of azodicarboxylates. The sodium cyanoborohydride and sodium borohydride reductions to thiadiazoles 11, and 12 were also studied. Plausible mechanistic schemes for the formation of the thiadiazoles are proposed.