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A chiral manganese porphyrin complex with a two-point hydrogen-bonding site was prepared and probed in catalytic C-H oxygenation reactions of 3,4-dihydroquinolones. The desired oxygenation occurred with perfect site selectivity at the C4 methylene group and with high enantioselectivity in favor of the respective 4S-configured secondary alcohols (12 examples, 29-97 % conversion, 19-68 % yield, 87-99 % ee). Mechanistic studies support the hypothesis that the reaction proceeds through a rate- and selectivity-determining attack of the reactive manganese oxo complex at the hydrogen-bound substrate and an oxygen transfer by a rebound mechanism.
Burg et al. (Sun,) studied this question.