Arenecarbaldehyde dimethylhydrazones were successfully acylated by trifluoroacetic anhydride to afford trifluoroacetylated hydrazones 2. Several 5-Aryl-6-trifluoromethyl-3,6-dihydro-2H-1,3,4-oxadiazines 3 were synthesized in good yields by novel cyclization of 2, thus obtained, using silica gel as an effective catalyst. Hydrolytic ring cleavage of 3 afforded α-hydroxyketones 5 bearing the trifluoromethyl group in high yields.
Several 6-trifluoromethyl-3,6-dihydro-2H-1,3,4-oxadiazines 2 were synthesized in good yields by treatment of trifluoroacetylated hydrazones 1, prepared from substituted benzaldehyde and alkanal dialkylhydrazones and trifluoroacetic anhydride, with trifluoroacetic acid at 25°C or acetic acid at 50°C. This is an improved method for the synthesis of 2 compared to previous methods developed in this laboratory.
Several 3-aryl-1,1,1-trifluoro-4,5-diaza-2,4-alkadienes 3 were synthesized in good yields from arenecarbaldehyde dimethylhydrazones 1 or its trifluoroacetylated derivatives 2 by reaction with an excess of trifluoroacetic anhydride in pyridine. Acid hydrolysis of 3 afforded 1-aryl-3,3,3-trifluoro-1-propanones 4 in high yields.