A new synthesis of [2,3]naphthoporphyrins using 4,9-ethano-2H-benz[f]isoind
ole as a synthon of 2H-benz[f]- isoindole is described; soluble precursors
of [2,3]naphthoporphyrins are converted into insoluble [2,3]naphthoporphyri
ns by simply heating at 290 degrees C.