Alkoxy Radical Generation Mediated by Sulfoxide Cation Radicals for Alcohol-Directed Aliphatic C-H Functionalization.

The C-H functionalization of remote, unactivated C-H bonds offers a unique method of garnering structural complexity in a synthesis. The use of directing groups has provided a means of enacting C-H functionalization on these difficult-to-access bonds; however, the installation and removal of directing groups on a substrate require additional synthetic manipulations, detracting from both the efficiency and economic feasibility of a transformation. The use of alkoxy radicals as transient directing groups for the functionalization of remote C-H bonds allows access to the synthesis of complex molecules without the need for additional functionality. Herein, we report a method for alkoxy radical formation from unactivated alcohols and reactivity mediated by photoredox-generated sulfoxide cation radicals. This protocol leverages the unique reactivity of alkoxy radicals to implement different reaction manifolds: 1,5-hydrogen atom transfer (HAT), cyclization, and β-scission. Furthermore, it was discovered that this methodology could be utilized to impose radical group transfer reactions via the β-scission pathway. Stern-Volmer analysis supports the formation of an alkoxy radical via the intermediacy of a sulfurane radical rather than a proton-coupled electron transfer (PCET) mechanism.