Efficient synthesis of 5-fluoroalkylated 1H-1,2,3-triazoles and application of the bromodifluoromethylated triazole to the synthesis of novel bicyclic gem-difluorinated 1H-pyrano[3,4-d][1,2,3]-triazol-4-one compounds

A series of 5-fluoroalkylated 1H-1,2,3-triazoles were synthesized in good yield by the regiospecific 1,3-dipolar cycloaddition reaction of (Z)-ethyl 3-fluoroalkyl-3-pyrrolidino-acrylates with aryl or benzyl azides. In the cases of benzyl azides, addition of Na2CO3 was crucial for a high yield of the triazoles. Tetrakis(dimethylamino)ethylene (TDAE) promoted reaction of bromodifluoro-methylated triazole with aldehydes affording a new class of β,β-difluoro-β-triazolyl alcohol derivatives, which were lactonized with catalytic amount of p-toluenesulfonic acid in toluene at 80–90°C to give a series of novel bicyclic gem-difluorinated 1H-pyrano[3,4-d][1,2,3]-triazol-4-one compounds in good yield.