Scandium-Bipyridin-katalysierte, enantioselektive Addition von Alkoholen und Aminen anmeso-Epoxide

Cu(2+), Zn(2+), and Ni(2+) Complexes of C2-Symmetric Pseudopeptides with an Aromatic Central Spacer

Two new tetradentate C2-symmetric pseudopeptidic ligands derived from Val and Phe containing two amino and two amido groups and a central o-substituted aromatic spacer have been prepared. Their complexes with Cu(2+), Zn(2+), and Ni(2+) have been studied by potentiometry, UV-vis spectrophotometry, FT-IR, and ESI-MS. The presence of the aromatic spacer provides Cu(2+) complexes with stability constants several orders of magnitude higher than those observed for related ligands containing aliphatic central spacers. Besides, the formation of [MH-2L] complex species is favored. Crystal structures for the corresponding Cu(2+) and Ni(2+) have been obtained, revealing the metal atom in an essentially square-planar geometry, although, in several instances, the oxygen atom of an amide carbonyl of a second complex species can act as a fifth coordination site. In the case of Zn(2+), the only crystal structure obtained displays a square-pyramidal arrangement of the metal center. Finally, preliminary experiments show the catalytic activity of some of these complexes, in particular, Zn(2+) complexes, for epoxide ring-opening with using aniline as the nucleophile in a ligand accelerated process.

Enantioselective syntheses of β-amino alcohols catalyzed by recyclable chiral Fe(iii) metal complex

An efficient asymmetric desymmetrization of meso-epoxides with anilines catalyzed by a series of simple and environmentally benign in situ generated Fe(iii) complexes based on chiral tridentate ligands L1–L7 was carried out at rt.

Kinetic resolution of 2,3-epoxy 3-aryl ketones via catalytic asymmetric ring-opening with pyrazole derivatives

A highly efficient catalytic kinetic resolution of 2,3-epoxy 3-aryl ketones via asymmetric ring-opening with pyrazole derivatives has been achieved by using a chiral N,N′-dioxide–Sc(iii) complex as the catalyst.

Tungsten-catalyzed regio- and enantioselective aminolysis of trans-2,3-epoxy alcohols: an entry to virtually enantiopure amino alcohols

The first catalytic enantioselective aminolysis of trans-2,3-epoxy alcohols has been accomplished. This stereospecific ring-opening process was efficiently promoted by a tungsten/bis(hydroxamic acid) catalytic system, furnishing various anti-3-amino-1,2-diols with excellent regiocontrol and high enantioselectivities (up to 95% ee). Moreover, virtually enantiopure 3-amino-1,2-diols could be obtained by the sequential combination of two reactions that both involve the use of a chiral catalyst.

Scandium–Bipyridine-Catalyzed Enantioselective Aminolysis ofmeso-Epoxides

The scandium-bipyridine-catalyzed enantioselective addition of anilines and O-alkyl hydroxylamines to meso-epoxides has been optimized and extended to a broad range of epoxides and amines. Whereas aromatic meso-epoxides generally furnished the corresponding 1,2-amino alcohols in excellent enantioselectivities, aliphatic meso-epoxides only gave rise to moderate enantioselectivities in the aminolysis. The catalyst loading may be lowered to just 5 mol% with only marginal effects on yield and enantioselectivity. A strong positive nonlinear effect has been observed, pointing to aggregation phenomena of the catalyst.

Indium–bipyridine-catalyzed, enantioselective thiolysis of meso-epoxides

The indium-bipyridine-catalyzed, enantioselective ring-opening of meso-epoxides with aliphatic and aromatic thiols furnished 1,2-mercapto alcohols in good yields and excellent enantioselectivities; the crystal structure of the chiral catalyst reveals a pentagonal-bipyramidal coordination geometry around the indium center.

Chiral Scandium Catalysts for Enantioselective Michael Reactions of β-Ketoesters

A highly enantioselective Michael reaction of beta-ketoesters with alpha,beta-unsaturated ketones promoted by a chiral scandium catalyst has been developed. In the presence of Sc(OTf)3 and (S,S)-6,6'-bis(1-hydroxy-2,2'-dimethylpropyl)-2,2'-bipyridine, the desired Michael reactions proceeded smoothly in dichloroethane at 40 degrees C to afford the corresponding adducts in good to high yields with excellent enantioselectivities in most cases. It was found in this reaction that a lower concentration of the reaction mixture was key to attaining high enantioselectivities.

Resolution of Racemic 2-Aminocyclohexanol Derivatives and Their Application as Ligands in Asymmetric Catalysis

A preparatively easy and efficient protocol for the resolution of racemic 2-aminocyclohexanol derivatives is described, delivering both enantiomers with >99% enantiomeric excess (ee) by sequential use of (R)- and (S)-mandelic acid. A simple aqueous workup procedure permits the isolation of the amino alcohols in analytically pure form and the almost quantitative recovery of mandelic acid. Debenzylation of enantiopure trans-2-(N-benzyl)amino-1-cyclohexanol by hydrogenation and subsequent derivatization give access to a broad variety of diversely substituted derivatives. Furthermore, the corresponding cis isomers are readily available. Applications of these optically active aminocyclohexanols in catalyzed asymmetric phenyl transfer reactions to benzaldehydes and transfer hydrogenations of aryl ketones lead to products with up to 96% ee.