Stereoselective synthesis of β-aryl-β-amino esters

Asymmetric Strecker synthesis of α-arylglycines

A practically simple three-component Strecker reaction for the asymmetric synthesis of enantiopure α-arylglycines has been developed. Addition of a range of aryl-aldehydes to a solution of sodium cyanide and (S)-1-(4-methoxyphenyl)ethylamine affords highly crystalline (S,S)-α-aminonitriles that are easily obtained in diastereomerically pure form. Heating the resultant (S,S)-α-aminonitriles in 6 M aqueous HCl at reflux resulted in cleavage of their chiral auxiliary fragments and concomitant hydrolysis of their nitrile groups to afford enantiopure (S)-α-arylglycines. The enantiopurities of these (S)-α-arylglycines were determined via derivatization of their corresponding methyl esters with 2-formylphenylboronic acid and (S)-BINOL, followed by (1)H NMR spectroscopic analysis of the resultant mixtures of diastereomeric iminoboronate esters.

4-(2-Carb-oxy-vin-yl)pyridinium iodide

In the crystal structure of the title salt, C(8)H(8)NO(2) (+)·I(-), the cations and anions are linked by bifurcated N-H⋯(O,I) hydrogen bonds. A near-linear O-H⋯I hydrogen bond also exists between the cation and anion, resulting in a two-dimensional network. In the cation, the carboxyl group is twisted with respect to the pyridine ring at a dihedral angle of 15.34 (17)°.

2-Carb-oxy-1-(3-nitro-phen-yl)ethanaminium perchlorate

In the title compound, C(9)H(11)N(2)O(4) (+)·ClO(4) (-), the organic cations form centrosymmetric dimers via a pair of O-H⋯O hydrogen bonds between the carboxyl groups. In the crystal, N-H⋯O inter-actions between the protonated amine group and the perchlorate anions and the nitro group connect the components into a two-dimensional network parallel to (001).

2-Carb-oxy-1-(3-nitro-phen-yl)ethanaminium perchlorate

In the cation of the title compound, C(9)H(11)N(2)O(4) (+)·ClO(4) (-), the conformation is stabilized by an intra-molecular N-H⋯O hydrogen bond. In the crystal packing, centrosymmetrically related cations inter-act through inter-molecular O-H⋯O hydrogen bonds involving the carb-oxy groups, forming dimers. The dimers and the perchlorate anions are further linked into layers parallel to the ab plane by C-H⋯O and N-H⋯O hydrogen-bonding inter-actions.

2-Carboxy-1-phenylethanaminium perchlorate

In the title compound, C9H12NO2+·ClO4−, an intramolecular N—H...O interaction results in the formation of a six-membered ring having a twisted chair conformation. In the crystal structure, intermolecular O—H...O, N—H...O and C—H...O interactions link the molecules into a network. A weak C—H...π interaction is also found.

Oxonium 2-carb-oxy-3-(2-fur-yl)acrylate

In the title compound, H₃O⁺·C₈H₅O₅⁻, neighbouring cations and anions are linked by O—H⋯O hydrogen bonds, forming a one-dimensional chain framework along [001]. The crystal structure is further stabilized by π–π inter­actions, with centroid–centroid distances of 3.734 (3) Å.

catena-Poly[cadmium(II)-(μ-3-ammonio-3-phenyl-propanoato-κO:O')-di-μ-chlorido]

The title compound, [CdCl(2)(C(9)H(11)NO(2))](n), is a coordination polymer prepared by the hydro-thermal reaction of cadmium(II) chloride and 3-amino-3-phenyl-propanoic acid. Geometric parameters are in the usual ranges. The cadmium cation is octa-hedrally coordinated by four Cl atoms at equatorial sites and two O atoms from two ligands at the axial sites. The material is composed of one-dimensional extended polymeric chains in which two Cl atoms bridge Cd atoms. The crystal structure is stabilized by an intra-molecular N-H⋯O hydrogen bond.

Asymmetric Heterogeneous Catalysis

Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.

Synthesis of a β-Amino Acid Pharmacophore via a β-Lactam Intermediate

A stereoselective synthesis of (R)-beta-amino acid 1 via a beta-lactam intermediate is discussed.

Highly Diastereoselective Heterogeneously Catalyzed Hydrogenation of Enamines for the Synthesis of Chiral β-Amino Acid Derivatives

Pure (Z)-enamines readily prepared from beta-ketoesters and amides using (S)-phenylglycine amide were hydrogenated with very high diastereoselectivities (up to 200:1) using heterogeneous catalysis. Hydrogenolytic cleavage of the (S)-phenylglycine amide afforded the corresponding chiral beta-aminoesters and amides. The high geometrical purity of the (Z)-enamine and a simple activation procedure for the PtO2 catalyst are essential in achieving high selectivity.