Formation of chlorins and meso-substituted porphyrins through intramolecular nitrogen-carbon migration of N-substituted porphyrins

A series of N-substituted porphyrins were synthesized either by direct alkylation of the symmetrical porphyrins or from the unsymmetrical porphyrins obtained via MacDonald's procedure using the appropriate N-substituted dipyrromethanes. Depending upon the nature of the peripheral substitutions in the porphyrin system, the nickeI(II)-promoted rearrangement of these compounds gave either meso-substituted or unsubstituted Ni(II)porphyrins or chlorins. The chlorins and meso-substituted porphyrins were formed via the intramolecular migration of the N-substituent to carbon. This approach provides easy access for the synthesis of chlorins and the meso-substituted porphyrins, which are otherwise difficult to synthesize.