Thermal and acid-catalyzed transformations of 3H-pyrazoles obtained from diphenyldiazomethane and methyl phenylpropiolate
作者:A. A. Fedorov、Sh. E. Duisenbaev、V. V. Razin、M. A. Kuznetsov、E. Linden
DOI:10.1134/s1070428007020145
日期:2007.2
Reaction of diphenyldiazomethane with methyl phenylpropiolate in diethyl ether alongside the expected methyl triphenyl-3H-pyrazole-4- and -5-carboxylates (I and II) (38 and 24%) gave rise also to 8% of methyl 3,5-diphenyl- 1-(1-ethoxyethyl)-1H-pyrazole-4-carboxylate. The main thermolysis product obtained from 4-methoxycarbonyl derivative I was methyl 1,3,5-triphenyl-1H-pyrazole-4-carboxylate, whereas from regioisomer II formed predominantly methyl 4,4,5-triphenyl-4H-pyrazole-3-carboxylate and 1-methoxycarbonyl-2,3,3-triphenylcyclopropene that was a minor product of 3H-pyrazole I thermolysis. Addition of concn. H2SO4 to the solutions of methyl triphenyl-3H-pyrazole-4- and -5-carboxylates in AcOH resulted in fast regioselective isomerization of the 3H-pyrazole derivatives into the corresponding 4H-pyrazoles.