Pyrazolinyl and cyclopropyl derivatives of protoporphyrin IX and chlorins related to chlorophyll a

Diazomethane reacts regioselectively with peripheral vinyl substituents of pyropheophorbide a and purpurin-18 N-methylimide to produce corresponding 1′-pyrazolinyl-substituted derivatives as a main product. Similarly, treatment of protoporphyrin IX gave a mixture of mono- and di-substituted pyrazolinyl analogs, which were isolated as individual products. Thermolytic decomposition of the pyrazolinyl derivatives produced cyclopropyl-substituted chlorins and porphyrins. 1,3-Dipolar cycloaddition mechanisms of the formation of 1′-pyrazolinyl derivatives are discussed.