Big Break for Boron

Abstract

Chemistry![Figure][1] CREDIT: J. J. HIRNER ET AL., J. AM. CHEM. SOC. 136 (3 MARCH 2014) © 2014 AMERICAN CHEMICAL SOCIETY Boron-oxygen (B-O) bonds generally are fairly strong and unreactive, a property that is useful in the reliance of Suzuki coupling on selective reactivity of the B-C bonds in boronate esters. Hirner et al. have devised a catalyst that formally cleaves B-O bonds through their intramolecular addition across an alkyne. Reasoning that direct insertion of a metal into the bond would face too high an energy barrier, the authors implemented a dual activation strategy, targeting a mechanism in which gold coordination enhances the reactivity of the C-C triple bond while trifluoroacetate coordination to B stimulates transfer of the adjacent O group. The protocol furnished a diverse array of benzofuran products with a B substituent conveniently poised for further reactivity via Suzuki coupling or other elaborations. Moreover, the reaction is broadly tolerant of groups such as halogens, esters, and nitriles, and it manifests complementary site-selectivity to arene C-H borylation reactions. J. Am. Chem. Soc. 135 , 10.1021/ja500463p (2014). [1]: pending:yes