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Catalytic conjunctive cross-coupling enabled by metal-induced metallate rearrangement

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Science  01 Jan 2016:
Vol. 351, Issue 6268, pp. 70-74
DOI: 10.1126/science.aad6080

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A two-for-one twist on Suzuki coupling

The Suzuki-Miyaura coupling reaction is one of the most widely used ways of making carbon-carbon bonds. Essentially a palladium catalyst activates one carbon fragment and then links it to a second fragment pulled from boron. Zhang et al. now demonstrate a twist on the conventional pathway (see the Perspective by Fyfe and Watson). In their system, the palladium initially coaxes together two carbon fragments on one boron center. Then the catalyst stitches a second C-C bond to a third, external fragment. A chiral ligand renders the reaction highly enantio-selective.

Science, this issue p. 70; see also p. 26

Abstract

Transition metal catalysis plays a central role in contemporary organic synthesis. Considering the tremendously broad array of transition metal–catalyzed transformations, it is remarkable that the underlying elementary reaction steps are relatively few in number. Here, we describe an alternative to the organometallic transmetallation step that is common in many metal-catalyzed reactions, such as Suzuki-Miyaura coupling. Specifically, we demonstrate that vinyl boronic ester ate complexes, prepared by combining organoboronates and organolithium reagents, engage in palladium-induced metallate rearrangement wherein 1,2-migration of an alkyl or aryl group from boron to the vinyl α-carbon occurs concomitantly with C–Pd σ-bond formation. This elementary reaction enables a powerful cross-coupling reaction in which a chiral Pd catalyst merges three simple starting materials—an organolithium, an organoboronic ester, and an organotriflate—into chiral organoboronic esters with high enantioselectivity.

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