Photoinduced Boron‐Catalyzed Direct <i>α</i> ‐Aminoxylation of Carboxylic Acids

A boron‐catalyzed direct α ‐aminoxylation of carboxylic acids is developed, providing rapid access to unique β ‐amino acid analogs, namely α ‐(aminoxy)carboxylic acids. Upon visible‐light irradiation, catalytically generated diboron enediolates undergo photoexcitation and energy transfer to O ‐sulfonylhydroxylamines, causing a novel SO bond cleavage pathway. This reactivity of the O ‐sulfonylhydroxylamine contrasts sharply with the conventional NO bond cleavage typically induced by single‐electron reduction. The resulting N ‐oxyl radicals exhibit high reactivity, enabling the synthesis of sterically congested N ‐alkyl‐ α , α ‐disubstituted‐ α ‐(aminoxy)carboxylic acids. The protocol is applicable to the aminoxylation of pharmaceutical carboxylic acids. Beyond simple N ‐protected aminoxylating agents, α ‐amino acid‐derived variants are also applicable, allowing for the construction of di‐ and tripeptides. Furthermore, leveraging the direct use of carboxylic acids, sequential condensation with glycine methyl ester enabled straightforward peptide elongation.