LAUSR

Lighting the way to carbon borylation Boron substituents provide versatile reactivity, and their utility has been emerging in pharmaceutical contexts. Fawcett et al. show that visible light can induce replacement of carboxylic acid groups with boronate esters, which will ease their introduction into a wide variety of compounds. Once the acids are activated with phthalimide substituents, they can react with catecholborane dimers under illumination in amide solvents, with no need for catalysts or other additives. The reaction appears to proceed by radical chain propagation after photoinitiation. Science, this issue p. 283 Light facilitates the replacement of carboxylic acids with boron esters in the absence of metal catalysts. The conversion of widely available carboxylic acids into versatile boronic esters would be highly enabling for synthesis. We found 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 primary, secondary, and tertiary alkyl carboxylic acids as well as a diverse range of natural-product carboxylic acids, thereby demonstrating its broad utility and functional group tolerance.