Site-selective bromination of sp³ C-H bonds

A method for converting sp³ C-H to C-Br bonds using an N-methyl sulfamate directing group is described. The reaction employs Rh₂(oct)₄ and a mixture of NaBr and NaOCl and is performed in aqueous solution open to air. For all sulfamates examined, oxidation occurs with high selectivity at the γ-carbon, affording a uniquely predictable method for C-H bond halogenation. Results from a series of mechanistic experiments suggest that substrate oxidation likely proceeds by a radical chain process. Initial formation of an N-halogenated sulfamate followed by Rh-mediated homolysis generates an N-centered radical, which serves as the active oxidant.