Synthesis of 5-aryl-3-glycosylthio-4-phenyl-4H-1,2,4-triazoles and their acyclic analogs under conventional and microwave conditions

Under microwave irradiation (MWI), 4-phenyl-5-substituted-4H-1,2,4-triazole-3-thiol derivatives 7 and 8 were synthesized in a good yield by intramolecular cyclization of the aroyl phenyl thiosemicarbazides 5 and 6. The respective triazolylglycosides (Str-glycosides) 12-17 were obtained by reaction of triazoles 7 and 8 with glycosyl halides 9-11 in dry acetone in the presence of potassium carbonate as base under both conventional and MWI conditions. Alkylation of 7 and 8 with haloalchols 18-20 in boiling ethanolic solution containing sodium ethoxide as a base gave the corresponding alkylated analogs 21-26. MWI conditions led to higher yield in shorter reaction time than the conventional method. Treatment of 26 with tosyl chloride gave the unexpected product 29 and not 27 or 28. Oxidation of 26 with sodium metaperiodate afforded triazole 8 and not the aldehyde 30. Attempted glycosylation and alkylation of the phenolic OH group in triazole 8 were unsuccessful; this was proved by theoretical calculations using the AM1 semi-empirical method.