RECENT ADVANCES IN THE SYNTHESIS OF PORPHYRINS WITH 5-MEMBERED EXOCYCLIC RINGS

New approaches to the synthesis of petroporphyrins bearing five-membered exocyclic rings are described. The key intermediates in these studies were cyclopenta[b]pyrroles, which were synthesized in one step from cyclopentanone. Reaction with lead tetraacetate gave acetoxy derivatives and further acid-catalyzed condensation with alpha-unsubstituted pyrroles gave a series of 6-pyrrolylcyclopenta-[b]pyrroles in excellent yields. These dipyrrolic intermediates were converted into meso-beta-ethanoporphyrins in moderate to good yields by the MacDonald condensation and the b-bilene approach, and this work has led to a new synthesis of deoxophylloerythroetioporphyrin (DPEP). Ongoing studies directed toward the synthesis of methylethanoporphyrins and fused ring ''diDPEP's'' are also reported.