A general, modular method for the catalytic asymmetric synthesis of alkylboronate esters
Crafting chiral boron building blocks Carbon boron bonds are easily transformed into a wide variety of C C, C N, and C O bonds. With that flexibility in mind, Schmidt et al. show that nickel complexes can catalyze asymmetric alkylation of carbon centers adjacent to boron. This protocol creates chiral alkylboronates that function as stable precursors to numerous complex molecules. The reaction proceeds in stereo convergent fashion forming a single product from either mirror image of the a haloboronate reagent. Successive reactions can also create chains of adjacent chiral alkyl centers with stereochemistry set by the configuration of the ligand bound to nickel. Science, this issue p. 1265 Nickel catalyzes stereoconvergent alkylzinc addition to a haloboronates to form chiral alkylboronate building blocks. Alkylboron compounds are an important family of target molecules, serving as useful intermediates, as well as end points, in fields such as pharmaceutical science and organic chemistry. Facile transformation of carbon boron bonds into a wide variety of carbon X bonds (where X is, for example, carbon, nitrogen, oxygen, or a halogen) with stereochemical fidelity, renders the generation of enantioenriched alkylboronate esters a powerful tool in synthesis. Here we report the use of a chiral nickel catalyst to achieve stereoconvergent alkyl alkyl couplings of readily available racemic a haloboronates with organozinc reagents under mild conditions. We demonstrate that this method provides straightforward access to a diverse array of enantioenriched alkylboronate esters, in which boron is bound to a stereogenic carbon, and we highlight the utility of these compounds in synthesis.
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