Enantioselective hydroxylation of benzylic C–H bonds by D4-symmetric chiral oxoruthenium porphyrins†

A D4-symmetric chiral dioxoruthenium(VI) porphyrin can effect stoichiometric and catalytic enantioselective hydroxylation of benzylic C–H bonds to give enantioenriched aryl alcohols, the highest ee of 76% being attained in the catalytic oxidation of 4-ethyltoluene with 2,6-dichloropyridine N-oxide as terminal oxidant; the oxidations proceed via a rate-limiting H-atom abstraction to germinate a benzylic radical intermediate.