Exploration of fluoral hydrazones derived from carbohydrazides for the synthesis of trifluoromethylated heterocycles

The reaction of fluoral hydrate with carbohydrazides in methanol in the presence of molecular sieves (4 A) gave the desired N-acylated fluoral hydrazones (3a–f) in fair yields. Treatment of the latter with mercaptoacetic acid in benzene led to the corresponding 2-trifluoromethyl-1,3-thiazolidinone derivatives (4a–f), whereas the reaction with acetic anhydride gave 3-acetyl-2,3-dihydro-2-trifluoromethyl-1,3,4-oxadiazoles (5a–f). The structures of each type of product have been established by X-ray crystallography.