Ligand-Enabled γ-C(sp3)-H Hydroxylation of Free Amines with Aqueous Hydrogen Peroxide.

Abstract

Selective oxidation of the γ-C-H bonds from abundant amine feedstocks via palladium catalysis is a valuable transformation in synthesis and medicinal chemistry. Despite advances on this topic in the past decade, there remain two significant limitations: C-H activation of aliphatic amines requires an exogenous directing group except for sterically hindered α-tertiary amines, and a practical catalytic system for C(sp3)-H hydroxylation using a green oxidant, such as oxygen or aqueous hydrogen peroxide, has not been developed to date. Herein, we report a ligand-enabled selective γ-C(sp3)-H hydroxylation using sustainable aqueous hydrogen peroxide (7.5-10%, w/w). Enabled by a CarboxPyridone ligand, a series of primary amines (1°), piperidines, and morpholines (2°) were hydroxylated at the γ-position with excellent monoselectivity. This method provides an avenue for the synthesis of a wide range of amines, including γ-amino alcohols, β-amino acids, and azetidines. The retention of chirality in the reaction allows rapid access to chiral amines starting from the abundant chiral amine pool.