Rhodium-catalysed asymmetric allylic arylation of racemic halides with arylboronic acids

Csp2−Csp2 cross-coupling reactions between arylboronic acid and aryl halides are widely used in both academia and industry and are strategically important in the development of new agrochemicals and pharmaceuticals. Csp2−Csp3 cross-coupling reactions have been developed, but enantioselective variations are rare and simply retaining the stereochemistry is a problem. Here we report a highly enantioselective Csp2−Csp3 bond-forming method that couples arylboronic acids to racemic allyl chlorides. Both enantiomers of a cyclic chloride are converted into a single enantiomer of product via a dynamic kinetic asymmetric transformation. This Rh-catalysed method uses readily available and inexpensive building blocks and is mild and broadly applicable. For electron-deficient, electron-rich or ortho-substituted boronic acids better results are obtained with racemic allyl bromides. Oxygen substitution in the allyl halide is tolerated and the products can be functionalized to provide diverse building blocks. The approach fills a significant gap in the methods for catalytic asymmetric synthesis.