Abnormal Diels–Alder Reaction of Oxazoles with 4-Phenyl-3H-1,2,4-triazole-3,5(4H)-dione and Diethyl Azodicarboxylate, and X-Ray Crystal Structure of an Adduct

The reaction of substituted oxazoles with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (PTAD) or diethyl azodicarboxylate gave the corresponding 1,2,4-triazoline derivatives through formal [3+2] cycloaddition accompanying ring opening of oxazoles. The molecular structure of an adduct of 5-methoxy-4-methyl-2-(p-tolyl)oxazole with PTAD was determined by means of X-ray crystallography.