Strategies for the Efficient Synthesis of Biheterocyclic 5-[2-(Trifluoromethylheteroaryl)-ethyl]-1,3,4-oxadiazoles from Levulinic Acid

The synthesis of 5-[2-(trifluoromethylheteroaryl)-ethyl]-1,3,4-oxadiazoles derived from levulinic acid is reported. Cyclocondensations [4 + 1] between four different 5-[2-(trifluoromethylheteroaryl)propionylhydrazides derived from methyl 7,7,7-trifluoro-4-methoxy-6-oxo-4-heptenoate obtained from levulinic acid, and electrophilic orthoesters RC(OR1)3 (where R = H, Me, Ph) and CS2 were carried out in a mild medium. Good yields (69-96%) of isolated products were obtained. The structures of the new ethylene-spaced biheterocycles were characterized using 1H and 13C nuclear magnetic resonance (NMR) ...