Enabling α -Functionalization of Carboxylic Acids by Boron Compounds

Boron catalysis enabled the chemoselective α -functionalization of carboxylic acids in the presence of other carbonyl groups such as ketones, esters, and amides. The reversible formation of a B-O covalent bond between the carboxy group and the boron catalyst increases the acidity of α -proton in carboxylic acids, thereby facilitating deprotonation to form enolates, diboron enediolates, using mild organic bases. As a result, Mannich reaction, aldol reaction, α -amination, and α - trifluoromethylthiolation were successfully developed including enantioselective reactions. Moreover, boron-palladium and boron-iridium hybrid catalysis have been developed to promote the asymmetric O to C migratory allylation of allyl esters. Photoirradiation of the in-situ generated diboron enediolates induces single-electron transfer from photoexcited diboron enediolates to electron-accepting allylsulfones, promoting radical reaction to provide α -allylation products. © 2024 Society of Synthetic Organic Chemistry. All rights reserved.