Synthesis and helicity of optically active poly(N‐propargylphosphonamidates) having chiral phosphorus center

Novel chiral N‐propargylphosphonamidate monomers (HC?CCH₂NHP(?O)R? O? menthyl, 1 : R = CH₃, 2 : R = C₂H₅, 3 : R = n‐C₃H₇, 4 : R = Ph) were synthesized by the reaction of the corresponding phosphonic dichlorides with menthol and propargylamine. Pairs of diastereomeric monomers 1 – 4 with different ratios were obtained due to the chiral P‐center and menthyl group. One diastereomer could be separated from another one in the cases of monomers 1 and 2 . Polymerization of 1 – 4 with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] as a catalyst in CHCl₃ gave the polymers with number‐average molecular weights ranging from 5000 to 12,000 in 65–85%. Poly( 1 )–poly( 4 ) exhibited quantitative cis contents, and much larger specific rotations than 1 – 4 did in CHCl₃. The polymers showed an intense Cotton effect around 325 nm based on the conjugated polyacetylene backbone. It was indicated that the polymers took a helical structure with predominantly one‐handed screw sense, and intramolecular hydrogen bonding between P?O and N? H of the polymers contributed to the stability of the helical structure. Poly( 1a ) and poly( 2a ) decreased the CD intensity upon raising CH₃OH content in CHCl₃/CH₃OH. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1515–1524, 2007     

Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems

With amino acids as model systems, optically active sum frequency generation (OA-SFG) was used to probe the chirality of molecules with a chiral center and an intrinsically achiral chromophore in isotropic solution for the first time. Like that of circular dichroism (CD), the OA-SFG's near electronic resonance originates from the extrachromophoric chiral perturbation on the carboxyl chromophore. The difference in the relative strengths of OA-SFG and CD among different amino acids can be explained by the difference in the details of perturbations.     

Optically active polypyrazolylborate molybdenum complexes with aminophosphines as chiral ligands

The prochiral polypyrazolylborate complexes [R---B(3,5-X₂-pz)₃]Mo(CO)₂(NO) (R = pz, X = H; R = H, X = CH₃), react with the optically active aminophosphines L = (C₆H₅)₂PNR′CH(CH₃)(C₆H₅) (R′= H, CH₃), to give the monosubstitution products [R---B(3,5-X₂-pz)₃]Mo(CO)(NO)L, in which the metal atom is a new chiral center. The separation of the diastereoisomers, differing only in the Mo configuration, by preparative liquid chromatography and fractional crystallization is described, their CD and ¹H NMR spectra and their reactivities are discussed and compared with those of the cyclopentadienyl analogues.     

Optically active dendrimers based on the planar chiral ferrocene core

The new planar chiral racemic and enantiomerically enriched Frechet-type dendrimers of the first and second generations bearing one and two branches and 1,2-disubstituted ferrocene as the core moiety were synthesized. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1220–1222, June, 2008.     

Optically active polyelectrolyte multilayers as membranes for chiral separations

Ultrathin films of chiral polyelectrolyte complex, prepared by the multilayering process, exhibit selectivity in the membrane separations of optically active compounds, such as l- and d-ascorbic acid. The flux through these polyelectrolyte multilayers, PEMUs, is exceptionally high and may be controlled by the concentration of salt present in the permeating solutions. Both in-situ ATR-FTIR and chiral capillary electrochromatography indicate that flux selectivity is mainly kinetically controlled, stemming from a difference in diffusion rates of various enantiomers through PEMUs, rather than a difference in partitioning.     

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Polydimethylsiloxanes with part of the siloxane units bearing an optically active sulfoxide group were synthesized. These copolymers had chiral sulfur centres connected to the siloxane chain by a dimethylene bridge. They were obtained mostly by the kinetically controlled anionic ring-opening polymerization of 1-(2-organothioethyl)1,3,3,5,5-pentamethylcyclotrisiloxanes, followed by stereoselective oxidation of prochiral groups to yield partially enantiomeric sulfoxide groups. Sulfoxides bearing cyclic monomers were also used. Polymers were characterized by spectroscopy and polarimetry. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 879–888, 1997     

Optically active palladacycles containing imines derived from 1-(1-naphthyl)ethylamine: new resolving agents for P-chiral phosphines

The synthesis of the new palladium metallacycles containing imines derived from 1-(1-naphthyl)ethylamine is reported. These new organometallic complexes have been used to resolve the P-chiral ligand benzylcyclohexylphenylphosphine. The absolute configuration of (R_C,S_P)-[PdCl{2-[HCN-CH(Me)C₁₀H₆]-3-ClC₆H₃}(PBzCyPh)] has been determined by single crystal X-ray analysis.     

New chiral auxiliary: Optically active thiol derived from camphor

A new camphor based mercapto chiral auxiliary has been prepared, and demonstrated to induce very high chiral inductions in the diastereoselective reductions of -sulfinylketones, in the presence of bivalent Lewis acids.     

Optically active synthetic polymers as chiral stationary phases in HPLC

Synthetic, optically active polymers used as CSP are reviewed. The polymers are classified into three major categories, namely, addition polymers, condensation polymers, and cross-linked gels. The emphasis lies on polymethacrylates having helical conformation belonging to the first category. Helical polymethacrylates are synthesized using asymmetric anionic or radical polymerization techniques and show resolving ability towards a wide range of racemate.     

Optically active ruthenium porphyrins: chiral recognition and asymmetric catalysis

The current applications of ruthenium porphyrins in stoichiometric and catalytic asymmetric reactions are reported. Chiral recognition of racemic phosphines, isocyanides and amino esters has been studied by ¹H-NMR. Experimental investigations of the oxidation mechanism of racemic phosphines and amino esters are described. The stereochemistry of catalytic asymmetric oxidation and cyclopropanation of olefins with optically active ruthenium porphyrins are also discussed.     

Optically active dioxatetraazamacrocycles: chemoenzymatic syntheses and applications in chiral anion recognition

Two new C2 and D2 symmetrical dioxatetraaza 18-membered macrocycles [(R,R)-1 and (S,S,S,S)-2] are efficiently synthesized in enantiomerically pure forms by a chemoenzymatic method starting from (+/-)-trans-cyclohexane-1,2-diamine. The protonation constants and the binding constants with different chiral dicarboxylates are determined in aqueous solution by means of pH-metric titrations. The triprotonated form of (S,S,S,S)-2 shows moderate enantioselectivity with malate and tartrate anions (deltadeltaG=0.62 and 0.66 kcal mol(-1), respectively), being the strongest binding observed in both cases with the L enantiomer. Good enantiomeric discrimination is obtained with tetraprotonated (R,R)-1 and N-acetyl aspartate, the complex with the D-enantiomer being 0.92 kcalmol(-1) more stable than its diastereomeric counterpart. Despite the lack of enantioselectivity of tri- and tetraprotonated (R,R)-1 for the tartrate anion, a very good diastereopreference for meso-tartrate is found. All these experimental results allow us to propose a model for the host-guest structure based on coulombic interactions and hydrogen bonds.     

Optically active vibrations of lanthanum copper oxide compound (La2CuO4)

Normal coordinate analysis of the optically active vibrations of lanthanum copper oxide has been made, with the assumption of a perovskite K₂NiF₄ structural model. On the basis of the results of this treatment, all of the observed bands so far reported have been successfully assigned to the intramolecular CuO vibrations and the optically active lattice vibrations (the motions of La against CuO₆ octahedra, abbreviated to La---CuO₆). The force constants concerning CuO and LaO bonds have been obtained within the framework of the modified valence force fields. It has been found that the present normal coordinate analysis based on a whole crystal is useful for assigning the optically active vibrations (normal modes) at the center of the Brillouin zone in La₂ CuO₄.