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Catalyst-controlled doubly enantioconvergent coupling of racemic alkyl nucleophiles and electrophiles

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Science  31 Jan 2020:
Vol. 367, Issue 6477, pp. 559-564
DOI: 10.1126/science.aaz3855

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Convergent coupling

Metal-catalyzed coupling of two flat aromatic rings is one of the most versatile and widely applied chemical reactions. Efforts to extend this protocol to alkyl-alkyl coupling are complicated by the prospect of forming two different three-dimensional configurations at each carbon center, corresponding to four possible products. Huo et al. now report that a chiral nickel catalyst can convergently link two mirror-image pairs of alkyl reactants into just one product (see the Perspective by Xu and Watson). The specific reaction couples propargylic halides to zinc-activated aliphatic amides.

Science, this issue p. 559; see also p. 509

Abstract

Stereochemical control in the construction of carbon-carbon bonds between an alkyl electrophile and an alkyl nucleophile is a persistent challenge in organic synthesis. Classical substitution reactions via SN1 and SN2 pathways are limited in their ability to generate carbon-carbon bonds (inadequate scope, due to side reactions such as rearrangements and eliminations) and to control stereochemistry when beginning with readily available racemic starting materials (racemic products). Here, we report a chiral nickel catalyst that couples racemic electrophiles (propargylic halides) with racemic nucleophiles (β-zincated amides) to form carbon-carbon bonds in doubly stereoconvergent processes, affording a single stereoisomer of the product from two stereochemical mixtures of reactants.

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