Synthesis and chemistry of new benzoporphyrins

Benzoporphyrins 5and 6are the major products obtained from the cycloaddition reactions of β-fused metallo-pyrroloporphyrins 1and 2with dimethyl acetylenedicarboxylate. In the presence of excess dienophile a bis-adduct is also obtained which undergoes retro-Diels-Alder reaction to produce 5. Benzoporphyrin 5was converted into the first reported β-fused benzochlorins 9–11, and the free-base benzoporphyrin 12was regioselectively brominated to afford 13. Exhaustive bromination also yields hexabromobenzoporphyrin 14.