Syntheses of optically pure, conformationally constrained, and highly hydrophobic unusual amino acids: 2-amino-3, 3-diarylpropionic acids*

Diastereoselective and Enantioselective Synthesis of Unsymmetric β,β-Diaryl-α-Amino Acid Esters via Organocatalytic 1,6-Conjugate Addition of para-Quinone Methides

A novel strategy based on phase transfer catalysis for the diastereoselective and enantioselective direct assembly of unsymmetric β,β-diaryl-α-amino acid esters via 1,6-conjugate addition of para-quinone methides and glycine derivatives is described. This protocol also provides an alternative route to the synthetically interesting functionalized chiral tetrahydroisoquinoline and its analogues.

Asymmetric Synthesis of Non-Natural Amino Acid Derivatives: (2R/3S) and (2S/3R) 2-(Tert-Butoxycarbonylamino)-3-Cyclohexyl-3-Phenyl Propanoic Acids

Highly conformationally-constrained novel α-amino acid derivatives ((2R/3S) and (2S/3R)-2-(tert-butoxycarbonylamino)-3-cyclohexyl-3-phenylpropanoic acids) have been synthesised with high stereoselectivity (> 90% de) and in 36–37% overall yields. In the synthesis, Evans’ auxiliary (4(R/S)-4-phenyl-oxzaolidin-2-one) was used to control the stereoselectivity via the key reactions of asymmetric Michael addition, azidation and catalytic hydrogenolysis.

Catalytic, asymmetric, and stereodivergent synthesis of non-symmetric β,β-diaryl-α-amino acids

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.

Asymmetric synthesis of chiral 4-substituted 5,5-diethyl oxazolidin-2-ones as potential effective chiral auxiliaries

Four new chiral 4-substituted 5,5-diethyl oxazolidin-2-ones (5a-5d) as potential effective chiral auxiliaries were synthesized from readily available amino acids via asymmetric etherification, Boc protection, Grignard reaction and cyclization reactions in four steps with overall yields of 50-60%.