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Radical-polar crossover reactions of vinylboron ate complexes

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Science  03 Mar 2017:
Vol. 355, Issue 6328, pp. 936-938
DOI: 10.1126/science.aal3803

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Boron choreographs a double reaction

In the widely used Suzuki coupling reaction, boron surrenders an olefinic substituent to a metal catalyst en route to carbon-carbon bond formation. Kischkewitz et al. report a metal-free alternative pathway, wherein the boron stays bound to one end of the olefin while a carbon radical attacks the other end. Charge transfer then prompts migration of an alkyl or aryl group from the boron to form a second carbon-carbon bond. The boron can subsequently be displaced, generating a versatile array of alcohols, lactones, and quaternary carbon centers from simple precursors.

Science, this issue p. 936

Abstract

Vinyl boronic esters are valuable substrates for Suzuki-Miyaura cross-coupling reactions. However, boron-substituted alkenes have drawn little attention as radical acceptors, and the radical chemistry of vinylboron ate complexes is underexplored. We show here that carbon radicals add efficiently to vinylboron ate complexes and that their adduct radical anions undergo radical-polar crossover: A 1,2-alkyl/aryl shift from boron to the α-carbon sp2 center provides secondary or tertiary alkyl boronic esters. In contrast to the Suzuki-Miyaura coupling, a transition metal is not required, and two carbon-carbon bonds are formed. The valuable boronic ester moiety remains in the product and can be used in follow-up chemistry, enlarging the chemical space of the method. The cascade uses commercial starting materials and provides access to perfluoroalkylated alcohols, γ-lactones, γ-hydroxy alkylnitriles, and compounds bearing quaternary carbon centers.

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