Site-specific reduction of unsymmetrically substituted porphyrins to give isomerically pure chlorins
Abstract
Photoreduction, in the presence of ascorbic acid and diazabicyclo[2.2.2.]octane, of zinc(II) vinylporphyrins, affords vinylchlorins in which the macrocyclic double bond in the pyrrole subunit bearing the vinyl group is regioselectively cis-reduced; when a vinylporphyrin bearing a more strongly electron-withdrawing methoxycarbonyl group is photoreduced, the ester-bearing ring is regioselectively reduced.