Showing papers by "Vadim A. Soloshonok published in 2000"

Convenient, asymmetric synthesis of enantiomerically pure 2',6'- dimethyltyrosine (DMT) via alkylation of chiral equivalent of nucleophilic glycine

Abstract: Asymmetric synthesis of ( S )-2′,6′-dimethyltyrosine (DMT) via reactions of 4′-benzyloxy-2′,6′-dimethylbenzyl bromide with Ni(II)-complexes of the chiral Schiff base of glycine with ( S )- o -[ N -( N -benzylprolyl)amino]benzophenone was developed Inexpensive and readily available reagents and solvents involved, including recyclable chiral auxiliary, simplicity of the experimental procedures and high chemical yields, make this method synthetically attractive for preparing the target amino acids on a multi-gram scale

Rational design of highly diastereoselective, organic base-catalyzed, room-temperature Michael addition reactions.

Abstract: Via the rational design of a single-preferred transition state, stabilized by electron donor−acceptor-type attractive interactions, structural and geometric requirements for the corresponding starting compounds have been determined. The Ni(II) complex of the Schiff base of glycine with o-[N-α-picolylamino]acetophenone, as a nucleophilic glycine equivalent, and N-(trans-enoyl)oxazolidin-2-ones, as derivatives of an α,β-unsaturated carboxylic acid, were found to be the substrates of choice featuring geometric/conformational homogeneity and high reactivity. The corresponding Michael addition reactions were found to proceed at room temperature in the presence of catalytic amounts of DBU to afford quantitatively the addition products with virtually complete diastereoselectivity. Acidic decomposition of the products followed by treatment of the reaction mixture with NH4OH gave rise to the diastereomerically pure 3-substituted pyroglutamic acids.

(S)- or (R)-3-(E-Enoyl)-4-phenyl-1,3-oxazolidin-2-ones: Ideal Michael Acceptors to Afford a Virtually Complete Control of Simple and Face Diastereoselectivity in Addition Reactions with Glycine Derivatives.

Abstract: [formula: see text] Enantiomerically pure (S)- or (R)-3-(E-enoyl)-4-phenyl-1,3-oxazolidin-2-ones were found to serve as ideal Michael acceptors in addition reactions with achiral Ni(II) complexes of glycine Schiff bases. Virtually complete control of simple and face diastereoselectivity, observed in these reactions, combined with quantitative chemical yields renders this methodology synthetically superior to the previous methods.

Asymmetric Michael Addition Reactions of Chiral Ni(II)-Complex of Glycine with (N-trans-Enoyl)oxazolidines: Improved Reactivity and Stereochemical Outcome.

Abstract: Application of the ( N - trans -enoyl)oxazolidines as Michael acceptors in the kinetically controlled additions with a Ni(II)-complex of the chiral Schiff base of glycine with ( S )- o -[ N -( N -benzylprolyl)amino]benzophenone 1 was shown to be synthetically advantageous over the alkyl enoylates, allowing for remarkable improvement in reactivity and, in most cases, diastereoselectivity of the reactions. While the stereochemical outcome of the Michael additions of the aliphatic ( N - trans -enoyl)oxazolidines with complex 1 depended on the steric bulk of the alkyl group on the starting oxazolidines, the diastereoselectivity of the aromatic ( N - trans -enoyl)oxazolidines reactions was found to be controlled by the electronic properties of the aryl ring. In particular, the additions of complex 1 with ( N -cinnamoyl)oxazolidines, bearing electron-withdrawing substituents on the phenyl ring, afforded the (2 S ,3 R )-configured products with synthetically useful selectivity and in quantitative chemical yield, thus allowing an efficient access to sterically constrained β-substituted pyroglutamic acids and related compounds.

2,2,5,5,8,8-Hexa­methyl-2,3,5,6,7,8-hexa­hydro­imidazo­[1,2-a]­pyrazine-3,6-dione, a bicyclic product of α-amino­isobutyric acid condensation

Abstract: The title compound, C12H19N3O2, is an unusual product of silica-catalyzed intermolecular condensation of α-amino­isobutyric acid. The mol­ecule has three types of C—N bonds: a double bond, a cis-amide bond and single bonds, two of which are typical and two having intermediate lengths due to π-electron delocalization between C=N and C=O groups. The cis-amide moieties interact to form dimers via hydrogen bonds which stack in parallel layers.