Chemoselective Aliphatic C–H Bond Oxidation Enabled by Polarity Reversal

Abstract

Methods for selective oxidation of aliphatic C−H bonds are called on to revolutionize organic synthesis by providing novel and more efficient paths. Realization of this goal requires the discovery of mechanisms that can alter in a predictable manner the innate reactivity of these bonds. Ideally, these mechanisms need to make oxidation of aliphatic C−H bonds, which are recognized as relatively inert, compatible with the presence of electron rich functional groups that are highly
\nsusceptible to oxidation. Furthermore, predictable modification of the relative reactivity of different C−H bonds within a molecule would enable rapid diversification of the resulting oxidation products. Herein we show that by engaging in hydrogen bonding, fluorinated alcohols exert a polarity reversal on electron rich functional groups, directing iron and manganese catalyzed oxidation toward a priori stronger and unactivated C−H bonds. As a result, selective hydroxylation of methylenic sites in hydrocarbons and remote aliphatic C−H oxidation of otherwise sensitive alcohol, ether, amide, and amine substrates is achieved employing aqueous hydrogen peroxide as oxidant. Oxidations occur in a predictable manner, with outstanding levels of product chemoselectivity, preserving the first-formed hydroxylation product, thus representing an extremely valuable tool for synthetic planning and development.