No abstract

We report a concise, enantio- and diastereoselective route to novel nonsymmetrically substituted N-protected β,β-diaryl-α-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)2RhBF4 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 β,β-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.

No abstract

The synthesis and investigation of a new family of anionic N-heterocyclic carbene (NHC) ligands, based on Nsulfonyliminoimidazolium ylides, is reported. Their corresponding silver complexes have been synthesized and present distinctive geometries compared to the previously reported ligands derived from the N-acyliminoimidazolium family. A comparison of the two ligand families was performed with palladium(II) allyl complexes to investigate their binding mode preference. The N-sulfonyl derived ligands were found to strongly favor bridging binding instead of chelation. This strong preference was exploited to synthesize a novel copper(I)−palladium(II) heterotrimetallic complex.