A new synthesis of benzoporphyrins using 4,7-dihydro-4,7-ethano-2H-isoindole as a synthon of isoindole

Heating 4,7-dihydro-4,7-ethano-2H-isoindole at 200 °C induces the retro-Diels–Alder reaction to give isoindole in essentially quantitative yield, which can be applied to a new synthesis of tetrabenzoporphyrins and monobenzoporphyrins.