Ready Syntheses of Benzoporphyrins via Diels-Alder Reactions with Protoporphyrins IX
Morgan, A.R., Scherrer-Pangka, V., and David Dolphin
J. Chem. Soc.
Protoporphyrin IX di-Me ester (I) underwent Diels-Alder reaction with strongly activated dienophiles; the resulting adducts underwent elimination of the angular Me group to give monobenzoporphyrins. E.g., reaction of I with MeO2CC?CCO2Me (II) gave the adduct III, which rearranged to IV on treatment with Et3N. IV aromatized on treatment with excess II and Et3N to give the benzoporphyrin V.