Facile syntheses of modified tripyrranes and their application to the syntheses of regioisomerically pure porphyrin derivatives

Simple conditions were discovered to afford tripyrranes by reaction of 2,5-bis(alpha-hydroxymethyl)furan or 2,5-bis(alpha-hydroxy-alpha-phenylmethyl)thiophene with excess pyrrole in the presence of acid catalyst. Stepwise synthesis of porphyrins with core-ligand modification and synthesis of meso-tetraarylporphyrins bearing two different substituents in cis orientation have developed as building blocks for the various porphyrin-based model systems. Consequently, 21-thia-23-oxa-10,15-diphenylporphyrin (28), 21-oxa-10,15-diphenylporphyrin (29) and 21-oxa-23-carba-12-aza-10,15-diphenylporphyrin (30) were synthesized by acid-catalyzed [3+1] condensation between tripyrranes and 2,5-bis(a-hydroxymethyl)pyrrole or 2,5-bis(alpha-hydroxy-alpha-phenylmethyl)thiophene. The synthetic pathway described here gave regioisomerically pure porphyrins and thus overcame the synthetic problems associated with separation and purification of regioisomeric mixture.