Structural requirements in chiral diphosphine-rhodium complexes. VIII. Asymmetric hydrogenation of N-acetyldehydroamino acids with rhodium(I) complexes containing chiral carbocyclic analogues of DIOP.

Z--acetamidocinnamic acid was hydrogenated with neutral diphosphine-rhodium(I) complexes containing trans-1,2-bis(diphenylphosphinomethyl) cycloalkanes to give N-acetylphenylalanine: 86 % e.e.-(R) [(1R,2R)-cyclobutane]; 63 % e.e.-(R) [(1R,2R)-cyclopentane]; 35 % e.e.-(S) [(1S,2S)-cyclohexane]; and 82 % e.e.-(R) [(2R,3R)-DIOP]. Similarly, -acetamidoacrylic acid was hydrogenated to give N-acetylalanine: 72 % e.e.-(R) [(1R,2R)-cyclobutane]; 72 % e.e.-(R) [(1R,2R)-cyclopentane]; 40 % e.e.-(S) [(1S,2S)-cyclohexane]; and 73 % e.e.-(R) [(2R,3R)-DIOP].     

Aqueous enantioselective hydrogenation of methyl 2-acetamidoacrylate with Rh-MeDuPHOS occluded in PDMS

A new chiral heterogeneous catalytic system obtained by occlusion of the Rh-MeDuPHOS complex in a polydimethylsiloxane film was tested in the asymmetric hydrogenation of methyl 2-acetamidoacrylate in aqueous medium.     

Intermediates in asymmetric hydrogenation : The structure and 31P NMR spectra of rhodium enamide complexes containing 1R, 2R-trans-1,2-bis (diphenylphosphinomethyl) cyclo buta

Hydrogenation of bicyclo[2.2.1]heptadiene-1R,2R-(trans-1,2-bis(diphenylphosphinomethyl)cyclbutane rhodium (I) tetrafluoroborate in methanol gives a solvent adduct which reacts with N-acyldehydroamino acids and their esters to give air-unstable scarlet to yellow complexes. Effects of structure variation in the enamide on the ³¹P NMR spectra of these species are reported and discussed with reference to (a) the equilibrium between methanol and enamide complexes; (b) the ratio of diastereomeric enamide complexes formed; (c) the temperature dependence of this ratio; (d) the rate of complexation equilibria and (e) the structure of enamide complexes, which are normally bidentate with binding via the olefin and amide groups. In certain cases the complex may be terdentate and E-enamides bind through the olefin and carboxyl groups. Each mode of binding gives rise to characteristic ³¹P NMR spectra with regard to P-P and P-Rh coupling constants.     

The solid-state structure of (+)-(i)-menthyl 2-formamido-4, 4,4-trifluorobutanoate and the hydrogenation of the 2-butenoate precursor

Hydrogenation ofZ-(–)-(1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by Pd/C was performed at atmospheric pressure to yield a mixture of (2R, 1R, 3R, 4S)- and (2S, 1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluorobutanoate diastereomers in a 5545 ratio, respectively. Repeated fractional crystallization from ethyl acetate and vapor diffusion of petroleum ether afforded (+)–(2S, 1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluorobutanoate as clear colorless, crystalline prisms which were subjected to single-crystal X-ray diffraction analysis. The crystals belong to the orthorhombic system P2₁2₁2₁, and at 213 K:a=5.054(1),b= 10.000(2),c=32.707(1) Å,V=1652.9(4) ų,Z=4,R(F)=0.040, andR _w (F)=0.037. The finding of the (2S)-configuration for the formamido-acid portion of the (+)-ester enabled the configurational assignment of the asymmetric hydrogenation products ofZ-methyl 2-formamido-4, 4,4-trifluoro-2-butenoate catalyzed by chiral diphosphine/rhodium(I) complexes.     

Structural requirements in chiral diphosphine-rhodium complexes—XIII: Steric and electronic factors in the asymmetric homogeneous hydrogenation of Z-α-acylaminocinnamic acids and esters catalyzed by rhodium(I) complexes

Z-α-acylaminocinnamic acids and esters were hydrogenated with rhodium(I) complexes containing (4R,5R) - trans - 4,5 - bis(diphenylphosphinomethyl) - 2,2 - dimethyl - 1,3 - dioxolan (DIOP). Increasing the steric bulk of the acyl function (NHCOR, where R is an alkyl moiety) resulted in a lowered reduction of the si-re prochiral face to yield a decreasing excess of the (R)-amino acid derivatives. In the series of N-acylphenylalanine free acids (resulting from hydrogenation of Z-α-acylaminocinnamic acids) the optical purity decreased from 82% ee-(R) [Me]; 57% ee-(R) [i-Pr]; 52% ee-(R) [t-Bu]; to 46% ee-(R) [1-adamantyl]. Theα-benzamido, α-formamido and α-trifluoroacetamido substrates gave hydrogenation products having 68% ee-(R) [Ph]; 60% ee-(R) [H]; and 16% ee-(R)[CF₃]. In the corresponding methyl esters, increasing the steric bulk of the acyl function (NHCOR) resulted in a markedly greater decrease in enantioface differentiation. In the series of N-acylphenylalanine methyl ester products (resulting from hydrogenation of Z-methyl α-acylaminocinnamates) the optical purity decreased from 69% ee-(R)[Me]; 15% ee-(R) [i-Pr]; to 0% ee[t-Bu and 1-adamantyl]. The α-benzamido, α-formamido, and α-trifluoroacetamido substrates gave hydrogenation products having 36% ee-(R) [Ph]; 58% ee-(R) [H]; and 22% ee-(S) [CF₃]In the series of N-acetylphenylalanine alkyl ester products (resulting from hydrogenation of Z-alkyl α-acetamidocinnamate esters) trifluoro substitution in the alkyl alcohol moiety resulted in a decrease in optical purity to 52% ee-(R) [CH₂CF₃] compared to 72, 76 and 77% ee-(R) [Et, i-Pr and t-Bu, respectively].     

A novel system consisting of Rh-DuPHOS and ionic liquid for asymmetric hydrogenations

The ionic liquid [bmim][PF6] was found to provide extra stability to the air-sensitive chiral catalyst Rh-MeDuPHOS in asymmetric hydrogenation of enamides.     

On the mechanism of intramolecular photocycloaddition of substituted o-allylphenols to cyclic ethers

Osmometric and NMR techniques were used in order to study the ionic mechanism for the intramolecular photocycloaddition reaction of o-allyl phenols (1) to give cyclic ethers (2) + (3). The role of the intramolecular H-bond between the OH group and the π-electrons of the allylic group was ascertained. based on the results of the photocyclization, osmometric and NMR measurements the substituents can be divided into 3 groups according to their effect on the above intramolecular interaction.     

Enzymatic synthesis ofS-adenosyl-l-methionine froml-methionine and ATP

S-Adenosyl-L-methionine (SAM) has been synthesized on 7-mmol scale from L-methionine and ATP. The ATP was generated in situ from AMP, and the synthesis of SAM was catalyzed by the enzyme ATP:L-methionine S-adenosyltransferase (EC 2.5.1.6). Although substantial effort was required to obtain even small quantities of enzyme, it has good stability once isolated and immobilized. The SAM produced by this procedure contains 89% of the (-) diasterioisomer and 11% of the (+) diasterioisomer.     

Chemically Crosslinked Polysaccharide of the Red Microalga Rhodella Reticulata - An Ion Exchanger for Toxic Metal Ions 1

The structure and physicochemical properties of the sulfated polysaccharides that encapsulate cells of the red microalgae have been studied in our laboratory for a number of years with the aim of evaluating their potential applications.^2-6 Exploitation of the charged groups of these heteropolymers as chelating agents could provide an environmentally friendly means of disposing of toxic metals in industrial wastes. Ion exchangers and affinity absorbents may be prepared by crosslinking polysaccharides with epichlorhydrin, for example, mucopolysaccharides can bind polyvalent ions.^7-9