Approaches to the stepwise synthesis of benzoporphyrins and phthalocyanines. Part 1. Synthesis of opp-dibenzoporphyrins (dibenzo[g,q]porphyrins)

A stepwise synthesis of the opp-dibenzoporphyrin (dibenzo[g,q]porphyrin) system involving isoindole precursors is described. 3-Halogeno-1-formylisoindoles are condensed with various α-unsubstituted pyrroles to give the corresponding benzopyrromethene hydrobromides. Thermal self-condensation of such compounds bearing an α-methyl group gives the corresponding opp-dibenzoporphyrin derivatives in low to modest yields depending on the β-substitution pattern of the original pyrrole component.