Zinc (I1) porphyrins bearing unsubstituted fl positions can be mercurated at the 4 position and at an adjacent meso position. Palladium/olefin reactions with the dimercurated porphyrins produce products possessing a five-membered isocyclic ring bridging the fl and meso positions and resembling that found in chlorophyll derivatives. With use of this methodology, novel syntheses of deoxophylloerythroetioporphyrin (2) and ...