Science 2014-07-25

Dual catalysis. Single-electron transmetalation in organoboron cross-coupling by photoredox/nickel dual catalysis.

John C Tellis, David N Primer, Gary A Molander

Index: Science 345(6195) , 433-6, (2014)

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Abstract

The routine application of C(sp3)-hybridized nucleophiles in cross-coupling reactions remains an unsolved challenge in organic chemistry. The sluggish transmetalation rates observed for the preferred organoboron reagents in such transformations are a consequence of the two-electron mechanism underlying the standard catalytic approach. We describe a mechanistically distinct single-electron transfer-based strategy for the activation of organoboron reagents toward transmetalation that exhibits complementary reactivity patterns. Application of an iridium photoredox catalyst in tandem with a nickel catalyst effects the cross-coupling of potassium alkoxyalkyl- and benzyltrifluoroborates with an array of aryl bromides under exceptionally mild conditions (visible light, ambient temperature, no strong base). The transformation has been extended to the asymmetric and stereoconvergent cross-coupling of a secondary benzyltrifluoroborate.Copyright © 2014, American Association for the Advancement of Science.