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Results describe methodology for synthesizing chiral bisphosphines for Ru-catalyzed asymmetric hydrogenation of beta-ketoesters. Data indicate that changing ligand dihedral angles of the bisphosphines produces variations in their enantioselectivity.

Research has been conducted on the chiral phosphine ligands.The development of the bisphosphine ligand as an effective ligand for the Rh-catalyzed enamides hydrogenation in the chiral amine preparation is described.

A practical synthetic route for chiral hydroxyl mono- and bisphospholane synthesis is described. Data suggest that the hydroxyl phospholanes accelerate the Baylis-Hillman reaction. Further, the Rh(I) complexes of bisphospholanes serve as catalysts for the enantioselective hydrogenation of unsaturated substrates.

A study concerning the hydrogenation of beta-(acylamino)acrylates for the synthesis of beta-amino acid derivatives is presented. The use of Rh-BICP and Rh-DuPhos catalytic systems is described.

A study was conducted to analyze the asymmetric rhodium-catalyzed hydrogenation of enamides with a chiral 1,4-bisphosphine bearing diphenylphosphino groups. Reactions were performed using a nitrogen-filled glovebox or standard Schelnk methods. Experimental results indicated that bis(diphenylphosphino)-1(R),1'(R)-dicyclopentane is one of the best chiral diphenylphosphino ligands for the rhodium-catalyzed asymmetric hydrogenation of electron-rich olefin substrates.

Research was conducted to examine the asymmetric formation of quaternary carbon centers catalyzed by novel chiral 2,5-dialkyl-7-phenyl-7-phosphabicyclo-(2.2.1)heptanes. Results indicate that phosphine 2,5-diakyl-7-phenyl-7-phosphabicyclo-(2.2.1)heptanes are one of the most effective catalysts for the asymmetric gamma-addition reaction. However, a rationale for the asymmetric C-C forming reaction could not be found.

The process of asymmetric hydrogenation of dehydroamino acids was thoroughly investigated. A new set of phosphinites, which could possibly produce nine-membered chelated complexes with rhodium, had remarkably high selectivities for the hydrogenation of dehydroamino acids. The main element in this process was that the two cyclopentane in the backbone restrict the conformational flexibility of the nine-membered ring and the four stereogenic carbon centers in the backbone determine the orientation of the four P-phenyl groups.

Aromatic aldehydes were utilized as a substrate for the Ti-catalyzed enantioselective addition of Et2Zn in the presence of a titanate complex with a tetradentate helical ligand. The asymmetric addition of diethylzinc to aldehydes for the synthesis of chiral secondary alcohols was dependent on (1R, 2R)-(+)-1,2-bis(3,5-dichloro-2-hydroxybenzenesulfonamido)(cyclohexane). The catalyst containing phenolic aromatic sulfonamide acted as monomeric titanate species during the asymmetric bond forming process.

A class of iron(II) porphyrins with unusually low CO to O2 affinity ratio was synthesized via the congruent multiple Michael addition method. Analysis of the nuclear magnetic resonance spectra of the myoglobin active site analogues indicated the role of steric interactions in reducing their CO to O2 affinity ratio. Furthermore, the low CO to O2 ratio was influenced by the structure of the porphyrin cavity and the steric effects of the axial ligand on Fe.

Reaction of 5,10,15, 20-tetrakis(2-hydroxyphenyl)porphyrin with ditosylthretiol derivatives produces nine compounds, which are members of a family of new chiral porphyrins. 1H NMR spectra and X-ray studies enable the identification of the resultant isomers. A comparative study of the epoxidation of unfunctionalized olefins, using manganese derivatives of these chiral porphyrins as catalysts, reveals that a manganese porphyrin generates up to 88% ee in the epoxidation of 1,2-dihydronaphthalene.

A surface acoustic wave (SAW) device that responds to oxygen pressure was developed by coating a 158-MHz quartz SAW device with an oxygen-binding agent. Two types of coatings were used. One type was prepared by dissolving an oxygen-binding agent in a toluene solution of a copolymer containing the axial ligand. A second type was prepared with an oxygen-binding porphyrin in a toluen solution containing excess axial ligand without a polymer matrix. In the polymer-based coatings, the copolymer served to provide the axial ligand to the oxygen-binding agent and as a coating matrix on the surface of the SAW device. The oxygen-sensing SAW device has been shown to bind oxygen following a Langmui isotherm and may be used to measure the equilibrium constant of the oxygen-binding compound in the coating matrix.

1H NMR and oxygen affinity analysis of iron and cobalt picnic basket porphyrins (PBP) reveals that PBPs have high oxygen affinities. Increase in basket size decreases oxygen affinity. Interactions between terminally bound dioxygen and amide protons influence oxygen affinity. The oxygen ligand in Co(II)O2 adducts has a greater electron density than that in Fe(II)O2 adducts.

Main observation and conclusion: Asymmetric hydrogenation reaction is one of the most efficient synthetic methods to form useful chiral compounds for synthetic chemistry, medicinal chemistry and material chemistry. Generally, the enantioselectivity of many hydrogenation reactions is controlled by steric hindrance between the chiral ligand and substrate. Recently, Zhang group developed a highly asymmetric hydrogenation of 2‐aryl and 2‐alkyl acrylic acids catalyzed by a Rh(I) catalyst with a chiral Wudaphos ligand. The excellent enantioselectivity of this asymmetric reaction was proposed to be controlled by ion‐pair interaction between the substrate and chiral ligand. In this study, a systematic density functional theory study has been carried out to investigate the reaction mechanism and origin of the enantioselectivity. Our computational results suggest that this reaction follows the classic mechanism involving oxidative addition of H2, migratory insertion and reductive elimination. Different from the C=C coordination to the metal in the common oxidative addition step, our study found that the chelation of the carboxyl group of the substrate to the cationic Rh(I) metal is more favorable in this oxidative addition step. The high enantioselectivity is proposed to be dictated by a better catalyst/substrate geometric complementarity in the major pathway to have less distortion of the catalyst for a strong ion‐pair interaction. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: The enantioselective hydrogenation of endocyclic enones has been a historical problem for homogeneous catalysis. We herein report an efficient method to reduce endocyclic enones with molecular hydrogen. Catalyzed by a rhodium/Zhaophos complex, a variety of enones with five‐, six‐ or seven‐member ring were hydrogenated with high enantioselectivity (92%—99% ee). Excellent chemo‐ and enantioselectivity demonstrated this method was successfully applied in the enantioselective hydrogenation of citral to produce enantio‐enriched citronellal. [ABSTRACT FROM AUTHOR]