Photoinduced decarboxylative borylation of carboxylic acids

The conversion of widely available carboxylic acids into versatile boronic esters would be highly enabling for synthesis. Here we report that this transformation can be effected by illuminating the N-hydroxyphthalimide ester derivative of the carboxylic acid under visible light at room temperature in the presence of the diboron reagent, bis(catecholato)diboron. A simple workup allows isolation of the pinacol boronic ester. Experimental evidence suggests that boryl radical intermediates are involved in the process. The methodology is illustrated by the transformation of not just primary, secondary, and tertiary alkyl carboxylic acids but also a diverse range of natural product carboxylic acids, thereby demonstrating its broad utility and functional-group tolerance.