Methods for selective benzylic C-H oxofunctionalization of organic compounds

The development of methods for the selective oxidation of C-H groups of organic compounds resulting in C-O bond formation is a challenging problem in modern synthetic organic chemistry. Versatile methods for the oxofunctionalization of these groups are currently lacking. Approaches for the oxidation of benzylic C-H groups having a relatively weak C-H bond (the homolytic bond dissociation energy is similar to 80 +/- 90 kcal mol(-1)) differ from the methods used for the oxidation of aliphatic and aromatic C-H groups with stronger C-H bonds. The review summarizes homogeneous catalytic and noncatalytic methods for the selective oxofunctionalization of benzylic groups of organic compounds developed in the past 40 years. Reactions using various oxidizing agents in the presence or in the absence of transition metal compounds are considered. Putative mechanisms of selected transformations are discussed. Particular focus is placed on the selective oxidation of various substrates.