V. I. Tararov

Asymmetric trimethylsilylcyanation of aldehydes catalyzed by chiral salen TiIV complexes with theC 1 symmetry

Asymmetric trimethylsilylcyanation of a number of aromatic and aliphatic aldehydes catalyzed by chiral TiIV complexes preparedin situ from Ti(OPri)4 and (1S)-[N,N′-bis(2′-hydroxy-3′-tert-butylbenzylidene)]-1,2-diaminoalkanes gives products with (S)-absolute configurations.

Asymmetric synthesis ofS-alkyl-substituted (R)-cysteinesvia a chiral NiII complex of the Schiff's base of dehydroalanine with (S)-2-N-(N-benzylprolyl)aminobenzophenone

An efficient procedure was developed for the asymmetric synthesis ofS-alkyl derivatives of (R)-cysteine by nucleophilic addition of alkanethiols (BunSH, ButSH, ortert-C5H11SH) to the C=C bond of the dehydroalanine fragment in the NiII complex of the Schiffs base of Δ-Ala with (S)-2-N-(N-benzylprolyl)aminobenzophenone [(S)-BPB-Δ-Ala]NiII. Under conditions of thermodynamic control of the reaction, the diastereomeric excess of the complexes with the (S.R)-configuration was 88–96%. After decomposition of the complexes,(R)-S-butylcysteine,(R)-S-tert-butylcysteine, and(R)-S-tert-pentylcysteine were isolated with an enantiomeric purity of >97%.

Asymmetric synthesis of β-N-substituted α,β-diamino acidsvia a chiral complex of NiII with a dehydroalanine derivative

Asymmetric synthesis of β-N-substituted (S)-α,β-diamino acids was accomplished by Michael addition of amines to the NiII complex of the Schiff base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and dehydroalamine. Diastereoselectivity of the reaction is kinetically and thermodynamically controlled. The chiral auxiliary reagent, BPB, can be recovered and reused.

Effects of the temperature and substituents in chiral TiIV(salen) catalysts on the enantioselectivity of the addition of Me3SiCN to PhCHO

The enantiomeric purity (ee) of the addition product of Me3SiCN to PhCHO at ∼20 °C catalyzed by chiral TiIV complexes, which were preparedin situ from Ti(OPri)4 and the Schiff bases (condensation products of substituted salicylaldehydes with (1R, 2R)-1,2-diaminocyclohexane), was, on the average, 20–30% lower than that achieved at −80 °C. The substituents at position 5 of 3-tert-butylsalicylaldehyde exert only the steric effect. It was shown that the stereochemical result of the reaction is controlled by the stage which involves the formation of the C−C bond rather than the transfer of the Me3Si group.

Asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by nucleophilic addition of triazolethiols to a NiII complex with a chiral dehydroalanine Schiff base

An efficient method was developed for the asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by the addition of 3,4-disubstituted 1,2,4-triazole-5-thiols at the electrophilic C=C bond in a NiII complex of a Schiff base of dehydroalanine with (S)-N-(N-benzylprolyl)aminobenzophenone. The stereoselectivity of the formation of diastereomeric complexes with the (S,R) configuration under conditions of thermodynamic control of the nucleophilic addition exceeds 94%. Acid treatment of the reaction mixtures afforded enantiomerically pure (R)-S-hetarylcysteines (ee >98%).

ON THE MECHANISM OF THE FE(CO)5-CATALYZED KHARASCH REACTION. 2. REINVESTIGATION OF STEREOCHEMISTRY OF BRCCL3 ADDITION TO METHYL N-ACRYLOYL-(S)-PROLINA TE

Addition of BrCCl3 to methylN-acryloyl-(S)-prolinate (1) catalyzed by Fe(CO)5 or Fe(CO)5-PPh3 at 75–80 °C in benzene solution affords in good total yield methylN-((S)-2-bromo-3,3,3-trichlorobutyryl)-(S)-prolinate (2) and methylN-((R)-2-bromo-3,3,3-trichlorobutyryl)-(S)-prolinate (3) in an ∼1.5 : 1 ratio, which does not depend on the catalytic system employed or its concentration. Catalysis by the Fe(CO)5-PPh3 system substantially increases the adducts yield.

Preparative asymmetric synthesis of (R)- and (S)-α-methylserine Ni(II) complex with a Schiff base of α-alanine and (S)-2-[(N-benzylprolyl)amino]benzophenone

The kinetic and thermodynamic diastereoselectivity of the hydroxymethylation of the alanine fragment in the Ni(II) complex of the Schiff base of alanine and (S)-2-[(N-benzylprolyl)amino]benzophenone (BBP) was studied. Optically pure (R)- and (S)-α-methylserines were synthesized.

Mechanism of hydrolysis of azalactones catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime

The hydrolysis of 2-methyl-4-benzyl-5(4H)oxazolone (MBA) in a mixture of water and MeCN has been studied — both the spontaneous reaction and that catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime (1). It has been shown that the complex 1 is an effective catalyst for the hydrolysis of MBA (chymotrypsin does not catalyze MBA hydrolysis). The mechanism of MBA hydrolysis catalyzed by this complex includes the formation of a mixed catalyst—substrate complex in which the MBA is coordinated with the metal ion through the N3 atom. It is suggested that the oxygen atom of the ionized oxime group in such a complex attacks the imine C2 atom of the MBA intramolecularly; this is the rate-determining stage. The change in the order of hydrolysis with respect to the catalyst from 1 to 1/2 when the concentration of 1 is increased indicates that the complex catalyst exists in aqueous solution in two forms, dimeric and monomeric, which are in equilibrium, and only the monomeric form of the complex is responsible for the catalysis. With an excess of the substrate we observe inhibition of the MBA hydrolysis — possibly an indirect indication of participation in the transition state by a water molecule coordinated in an apical position of the complex, which is displaced by excess substrate.

Synthesis of crosslinked polyacrylamide gel containing salicyl aldehyde fragments

The synthesis of 5-methacryloylamidosalicyl aldehyde is described. It yielded potassium Λ- and Δ-bis-[N-(5-methacryloylamidosalicylidene)-s-valinato] cobaltate (+3) (I) and cupric N-(5-methacryloylamidosalicylidene)-s-valinate (+2) (II). Copolymerization of I and II with acrylamide and N,N′-methylene-bis-acrylamide, followed by decomposition of the complexes, yielded hydrophilic polymers containing salicyl aldehyde fragments chemically bound to the polymeric matrix. The capacities of the polymers obtained with respect to the carbonyl group were determined.

Racemisation of amino acids under interphase catalysis conditions

Abstract A heterogeneous system, which effectively racemises amino acids in the presence of copper ions, has been obtained by the interaction of CG 400 I ion exchange resin in the OH− form with 4-decyloxysalicylaldehyde. The role of this system is shown to consist of: (a) heterogenisation of the reactive copper-Schiff base-amino acid complex with substituted salicylaldehyde; (b) heterogenisation of the racemisation-catalysing base; (c) increase of the local concentration of the base within the gel phase where the reactive copper complex is simultaneously concentrated.