Functionalization of 2,3-Disubstituted-2,3-dihydro-5,10,15,20-tetraphenylporphyrins

A reduced pyrrole subunit directs electrophilic functionalizations of dihydroporphyrins to the antipodal pyrrole ring by confining the chromophore 18-π-electron delocalization pathway to its N(22)H-N(24)H tautomer. The 2,3-disubstituents inhibit oxidation, this being exemplified by the synthesis of perbrominated dodecasubstituted metallochlorins. Regiospecific nitration (using N2O4) of metal-free chlorins provides access to Michael acceptors such as 12-nitro-2,3-disubstituted chlorins which are used in the preparation of highly functionalized tetraaryl-bacteriochlorins by conjugate addition of carbon-centered nucleophiles.