Effect of substituents in OsO₄ reactions of metallochlorins regioselective synthesis of isobacteriochlorins and bacteriochlorins

A first regioselective synthesis of bacteriochlorin by hydroxylation of metallated chlorin with OsO₄ is discussed. This is the first example for the preparation of metallobacteriochlorin. This methodology can also be used for the preparation of unsymmetrical isobacteriochlorins by introducing electron- withdrawing substituent(s) at the adjacent position(s) of the reduced ring. The Zn(II) vic-dihydroxybacteriochlorin obtained from 2-formyl-purpurin methyl ester showed long wavelength absorption at 828 nm which seems to be associated with electronic interactions of the substituents with the π- system of the macrocycle.