α‐Functionalization of Aliphatic Carboxylic Acid Equivalents via Direct CH Oxidation

Abstract The α‐functionalization of aliphatic carboxylic acids and equivalents thereof including amides and esters is among the highly important synthetic transformations of organic synthesis. Traditional approaches are largely dominated by enolate chemistry demanding (over) stoichiometric quantity of a strong base with respect to the carbonyl precursor to obtain a nucleophilic enolate equivalent and an electrophilic coupling partner to form a new CC and/or C–heteroatom bond. Modern progresses demonstrate that the α‐CH bond of carboxylic acids, amides, esters, and other synthons can be also triggered in the presence or absence of a transition metal catalyst under oxidative conditions. The external oxidant is known to play a crucial role in the α‐CH bond oxidation process. The current article describes the oxidative α‐CH bond functionalizations of carboxylic acids/equivalents by nucleophiles using transition metal catalysts or organic mediators. Consequently, (i) α‐CH transformations with the participation of an enolate equivalent from the carboxylate counterpart; (ii) Lewis acid‐catalyzed α‐functionalization approaches; (iii) α‐functionalization with concomitant decarboxylation, etc. are beyond the scope of this article.