Margarita A. Moskalenko

Catalytic Asymmetric Synthesis of O-Acetylcyanohydrins from Potassium Cyanide, Acetic Anhydride, and Aldehydes, Promoted by Chiral Salen Complexes of Titanium(IV) and Vanadium(V)

The utility of the chiral [Ti(μ-O)(salen)]2 complexes (R)- and (S)-1 (H2salen was prepared from (R,R)- or (S,S)-cyclohexane-1,2-diamine and 3,5-di(tert-butyl)-2-hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac2O to aldehydes to produce O-acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100 : 1 and produced the O-protected cyanohydrins with ee in the range of 60–92% at −40°. Other complexes, [Ti2(AcO)2(μ-O)(salen)2] ((R)-4) and [Ti(CF3COO)2(salen)] ((R)-5), were prepared from (R)-1 by treatment with different amounts of Ac2O and (CF3CO)2O, and their catalytic activities were tested under the same conditions. The efficiency of (R)-4 was found to be even greater than that of (R)-1, whereas (R)-5 was inactive. The synthesis of the corresponding salen complexes of VIV and VV, [V(O)(salen)] ((R)-2) and [V(O)(salen)(H2O)] [S(O)3OEt] ((R)-3), was elaborated, and their X-ray crystal structures were determined. The efficiency of (R)-3 was sufficient to produce O-acetyl derivatives of aromatic cyanohydrins with ee in the range of 80–91% at −40°.

Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

Stereochemically inert cationic cobalt(III) complexes were shown to be one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa carbon dioxide pressure. The optimal catalyst possessed an iodide counter anion and could be recycled. A catalytic cycle is proposed in which the ligand of the cobalt complexes acts as a hydrogen-bond donor, activating the epoxide towards ring opening by the halide anion and activating the carbon dioxide for subsequent reaction with the halo-alkoxide. No kinetic resolution was observed when terminal epoxides were used as substrates, but chalcone oxide underwent kinetic resolution.

Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN, Ac2O and aldehydes

A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive.

Tetraaryl-1,3-dioxolane-4,5-dimethanols as catalysts for the addition of trimethylsilyl cyanide to benzaldehyde and the oxirane ring

The synthesis of 1,2-, 1,3-, and 1,4-phenylene-bis[(4R,5R)-4,5-di(hydroxydiphenylmethyl)-1,3-dioxolane]s (ortho-, meta-, and para-bis-(R,R)-TADDOLs) and bis[4-{[(4R, 5R)-4,5-di(hydroxydiphenylmethyl)]-1,3-dioxolan-2-yl}phenyl]methane was carried out. The possibilities of the use of these compounds as catalysts for the C-C bond formation in the addition of Me3SiCN to benzaldehyde and the oxirane ring opening in cyclohexene oxide by Me3SiCN were investigated. The catalytic activity of different bis-(R, R)-TADDOLs in this series depends on their structure.

Using the same organocatalyst for asymmetric synthesis of both enantiomers of glutamic acid-derived Ni(II) complexes via 1,4-additions of achiral glycine and dehydroalanine Schiff base Ni(II) complexes.

Abstract(S)- and (R)-BIMBOL were efficient PT catalysts of asymmetric Michael addition of prochiral Ni–PBP–Gly (1) to acrylic esters and malonic esters to Ni–PBP–Δ-Ala (2) correspondingly. The salient feature of the catalysis is opposite configurations of Glu prepared via the two paths with BIMBOL of the same configuration and a perspective novel catalytic procedure for the synthesis of Gla derivatives.

Asymmetric opening of styrene oxide with p-toluidine catalyzed by BINOL polyols and their lithium complexes

Opening of racemic styrene oxide with p-toluidine catalyzed by chiral BINOL-derived polyols proceeded regioselectively mainly with the formation of 2-phenyl-2-(p-tolylamino)-ethanol with low ee values.

A mechanistic study of the Lewis acid–Brønsted base–Brønsted acid catalysed asymmetric Michael addition of diethyl malonate to cyclohexenone

The Michael addition of diethyl malonate (Michael Donor, MD) to cyclohexenone (Michael Acceptor, MA) catalysed by the mono-lithium salt of (S)- or (R)-BIMBOL in dichloromethane is shown to exhibit biomimetic behavior. A combination of kinetics, spectroscopic studies, synthesis of catalyst analogues, inhibition studies and DFT calculations are used to show that the catalyst activates both components of the reaction and uses a chain of proton transfers to facilitate the deprotonation of diethyl malonate. The initial reaction rate was first order relative to both MA and MD and 0.5 order relative to the catalyst, indicating that an equilibrium exists between monomeric and dimeric forms of the catalyst, with the dimer predominating, but only the monomeric form being catalytically active. This was supported by DOSY 1H NMR experiments. The importance of the Lewis acidic lithium cation in the catalytic step was established by complete inhibition of the reaction by lithium complexing agents. The importance of the number of OH-groups and their relative intramolecular orientation and acidities in the polyol catalyst was shown by studying the relative catalytic activities of catalyst analogues. DFT calculations allowed the relative energies and structures of the likely intermediates on the reaction coordinate to be calculated and indicated that the ionisation of MD was facilitated due to the Lewis acidity of the lithium cation and hydrogen bond formation between deprotonated MD (MD−1) and the OH groups of the BIMBOL moiety.

New bifunctional organocatalysts based on (R,R)-cyclohexane-1,2-diamine for the asymmetric addition of nucleophiles to aldehydes

The amide and sulfamide derivatives of (1R,2R)-N,N-diethylcyclohexane-1,2-diamine can serve as organocatalysts for addition of Me3SiCN and Et2Zn to aldehydes.

Phase-transfer enantioselective monoalkylation of prochiral nickel(ii) complexes catalyzed by 3,3′-bis[hydroxy(diphenyl)methyl]-1,1′-binaphthyl-2,23′-diol (BIMBOL) as a route to α-amino acids

An achiral nickel complex with a Schiff base derived from glycine was alkylated with alkyl halides under conditions of asymmetric phase-transfer catalysis. The chiral tetraol (R)-BIMBOL was employed as a catalyst. The enantiomeric purity of the alkylation products was up to 88%. Subsequent decomposition of the complexes afforded the corresponding a-amino acids.