A NEW METHOD FOR REGIOSPECIFIC DEUTERIATION AND REDUCTION OF 5,10,15,20-TETRAPHENYLPORPHYRINS - NUCLEOPHILIC REACTION OF BOROHYDRIDE ION WITH 2-NITRO-5,10,15,20-TETRAPHENYLPORPHYRINS

New methods for specific reduction and deuteriation of 5,10,15,20-tetraarylporphyrins are reported. Free-base and metalated 2-nitroporphyrins are converted into the corresponding nitrochlorins (2,3-dihydro-2-nitro-5,10,15,20-tetraphenyl-22H,24H-porphyrins) by reaction with borohydride followed by aqueous workup. These nitrochlorins may be readily converted into the denitrated chlorin by treatment with tributyltin hydride or into the corresponding denitrated porphyrin by elimination of nitrous acid by heating or treatment with silica. Deuterium labeling studies show that the formation of nitrochlorin from nitroporphyrin involves attack by hydride at the beta-pyrrolic carbon next to that bearing the nitro group followed by protonation of the resultant nitronate in aqueous workup. Specific deuteriation at the beta-pyrrolic next to that previously occupied by a nitro group is readily achieved by borodeuteride ion reaction with a 2-nitroporphyrin (50 atom % deuterium incorporation) or with a 2-methoxy-3-nitroporphyrin (100 atom % deuterium incorporation).