Syntheses of Regiospecifically Meso Functionalized Dipyrromethanes, Porphyrins, and Diphenylethane-linked Bisporphyrins

Acid catalyzed condensation of 2-unsubstituted pyrroles with diethyl acetals permits preparation, in good yields, of a variety of meso-functionalized dipyrromethanes. Subsequent use in the so-called MacDonald "2 + 2" condensation provides 5-functionalized porphyrins and, eventually, benzochlorin derivatives. A novel application of a reductive coupling scheme, utilizing Ni(0), provides diphenylethane-linked bisporphyrins, which are potential models for electron transfer studies.