New route to protoporphyrins III and XIII from common starting pyrroles

A new approach to protoporphyrins III (2′) and XIII (3′) has been developed based on a single set of starting materials, namely, 2,4-dimethyl-3-(2-chloroethyl)carbethoxypyrrole (4) and 3,3′-di(2-methoxycarbonylethyl)-4,4′-dimethyldipyrromethane-5,5′-dicarboxylic acid (5) for both targets. The biladiene route was adopted for the preparation of 2′ (five steps, 18% overall yield) while the coupling of two pyrromethenes was used to synthesize 3′ (four steps, 11% overall yield).