Catalyst- and solvent-free synthesis of 2-fluoro-N- (3-methylsulfanyl-1H-1,2,4-triazol-5-yl)benzamide through a microwave-assisted Fries rearrangement: X-ray structural and theoretical studies

An efficient approach for the regioselective synthesis of (5-amino-3-methyl­sulfanyl-1H-1,2,4-triazol-1-yl)(2-fluoro­phen­yl)methanone, C10H9FN4OS, (3), from the N-acyl­ation of 3-amino-5-methyl­sulfanyl-1H-1,2,4-triazole, (1), with 2-fluoro­benzoyl chloride has been developed. Heterocyclic amide (3) was used successfully as a strategic inter­mediate for the preparation of 2-fluoro-N-(3-methyl­sulfanyl-1H-1,2,4-triazol-5-yl)benzamide, C10H9FN4OS, (4), through a microwave-assisted Fries rearrangement under catalyst- and solvent-free conditions. Theoretical studies of the prototropy process of (1) and the Fries rearrangement of (3) to provide (4), involving the formation of an intimate ion pair as the key step, were carried out by density functional theory (DFT) calculations. The crystallographic analysis of the inter­molecular inter­actions and the energy frameworks based on the effects of the different mol­ecular con­formations of (3) and (4) are described.