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Journal of the American Chemical Society, Vol.137, No.2, 999-1006, 2015
Catalytic, Asymmetric, and Stereodivergent Synthesis of Non-Symmetric beta,beta-Diaryl-alpha-Amino Acids
We report a concise, enantio- and diastereoselective route to novel nonsymmetrically substituted N-protected beta,beta-diaryl-alpha-amino acids and esters, through the asymmetric hydrogenation of tetrasubstituted olefins, some of the most challenging examples in the field. Stereoselective generation of an E- or Z-enol tosylate, when combined with stereoretentive Suzuki-Miyaura cross-coupling and enantioselective hydrogenation catalyzed by (NBD)(2)RhBF4 and a Josiphos ligand, allows for full control over the two vicinal stereogenic centers. High yields and excellent enantioselectivities (up to 99% ee) were obtained for a variety of N-acetyl, N-methoxycarbonyl, and N-Boc beta,beta-diaryldehydroamino acids, containing a diverse and previously unreported series of heterocyclic and aryl substituted groups (24 examples) and allowing access to all four stereoisomers of these valuable building blocks.