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A radical approach to the copper oxidative addition problem: Trifluoromethylation of bromoarenes

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Science  01 Jun 2018:
Vol. 360, Issue 6392, pp. 1010-1014
DOI: 10.1126/science.aat4133

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Arenes get a light boost onto copper

Insertion of palladium into an aryl halide bond is the first step in numerous variants of cross-coupling chemistry used to make carbon-carbon bonds. Copper is an appealing alternative catalyst for such reactions because of its abundance and downstream reactivity profile. However, this preliminary step, termed oxidative addition, is often prohibitively slow for the cheaper metal. Le et al. report a photocatalytic way around this problem. A photoredox catalyst paired with a silane can activate aryl bromides to react with copper, likely via aryl radicals. The copper in this case then catalyzes trifluoromethylation of the arenes.

Science, this issue p. 1010

Abstract

Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.

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