Chiral Catalytic System Research Articles

Use of rhodium complexes with amphiphilic and nonamphiphilic ligands for the preparation of chiral α-aminophosphonic acid esters by hydrogenation in micellar media

Several kinds of micelle forming amphiphiles were tested in the asymmetric hydrogenation of the prochiral dialkyl 1-benzamido-2-phenyl-ethenephosphonates in aqueous media. The chiral catalytic system [Rh(cod) 2]BF 4/BPPM or amphiphilized PPM proved to be suitable for the hydrogenation reaction affording enantiomeric excesses up to 99%. A chiral induction is possible to a certain extent (up to 11% ee) by selected chiral amphiphiles in the presence of achiral rhodium catalysts.

Highly Enantioselective Catalytic Conjugate Addition and Tandem Conjugate Addition–Aldol Reactions of Organozinc Reagents

Although efficient catalysts for a number of asymmetric carbon carbon formations are known to date, a highly enantioselective catalytic version of the conjugate addition of organometallic reagents to enones is lacking. Recently chiral catalysts based on Cu, Ni, Zn, or Co complexes of a variety of ligands have shown enantioselectivities up to 90 % in 1,4additions of Grignard, organolithium, or dialkylzinc reagents. The results so far have not revealed, however, the key elements for realization of complete stereocontrol but do reveal the rather complex nature of some of these chiral catalytic systems. Previously we have demonstrated that copper complexes of chiral phosphorus amidites show relatively high ee values for the 1,4-adducts of R2Zn reagents and acyclic as well as cyclic enones. In this communication both the first catalytic asymmetric 1,4-addition reactions of organometallic reagents with complete

ChemInform Abstract: Asymmetric Synthesis of Amino Acids by Catalytic Reduction of Azlactones of Substituted Acylaminoacrylic Acids. Part 23. Reductive Aminolysis of 2‐Methyl‐4‐benzylidene‐δ2‐oxazolin‐5‐one (I) with the Chiral Catalytic System Pd/(S)‐Amino Alcohol, e.g. PdCl2/(S)‐(II).

ChemInform Abstract: Asymmetric Synthesis of Amino Acids by Catalytic Reduction of Azlactones of Substituted Acylaminoacrylic Acids. Part 23. Reductive Aminolysis of 2‐Methyl‐4‐benzylidene‐δ2‐oxazolin‐5‐one (I) with the Chiral Catalytic System Pd/(S)‐Amino Alcohol, e.g. PdCl2/(S)‐(II).

Asymmetric synthesis of amino acids by catalytic reduction of azlactones of substituted acylaminoacrylic acids. 23. Study of the reductive aminolysis of 2-methyl-4-benzyllidene-?2-oxazolin-5-one with the chiral catalytic system pd-s-aminoalcohol

1. Reductive aminolysis of 2-methyl-4-benzylidene-Δ2-oxazolin-5-one in the chiral catalytic system PdCl2-S-phenylglycinol results in the formation of phenylalanine amides with an excess of the SS-diastereomer. 2. Reductive aminolysis in the catalytic system PdCl2-S-phenylalaninol mainly gives phenylalanine amides with an excess of the RS-diasteromer.

Asymmetric hydrogenation of olefins on chiral cobalt catalytic systems

1. The Co(acac)2-PPh2(neomenthyl)-AlEt3 and Co(acac2-PPh2(O-menthyl)-AlEt3 systems are catalysts for the hydrogenation of styrene, 2-phenylbutenes, andα-ethoxystyrene and give low optical yields. 2. A possible mechanism is proposed for the hydrogenation and enantioselectivity of the catalyst action.

Asymmetric hydrogenation on chiral cobalt complexes

We were the first to effect the enantioselective hydrogenation of a mixture of isomeric 2-phenylbutenes on chiral cobalt catalytic systems of the Ziegler-Natta type in an optical yield of ∼25%.

Asymmetric synthesis of amino acids by the catalytic reduction of azlactones of protected acylaminoacrylic acids

1. Reductive methanolysis of 2-methyl-4-benzylideneoxazol-5-one in the presence of S-αp-henylethylamine, comprising hydrogenation of the C=C double bond and fission of the oxazolone ring, proceeds without the formation of intermediate products in quantity. 2. Z- and E-methyl esters of benzoylaminocinnamic acids on hydrogenation in the presence of a chiral catalytic system based on PdCl2 and S-α-phenylethylamine give the methyl esters of S- and R-benzoylphenylalanine, respectively. 3. Hydrogenation of E- and Z-benzoylaminocinnamic acids gives S- and R-benzoylphenylalanine, respectively.