Abstract Reaction of diphenyldiazomethane with methyl phenylpropiolate in diethyl ether alongside the expected methyl triphenyl-3 H-pyrazole-4-and-5-carboxylates (I and II)(38 and 24%) gave rise also to 8% of methyl 3, 5-diphenyl-1-(1-ethoxyethyl)-1 H-pyrazole-4- carboxylate. The main thermolysis product obtained from 4-methoxy-carbonyl derivative I was methyl 1, 3, 5-triphenyl-1 H-pyrazole-4-carboxylate, whereas from regioisomer II ...