Enantiomer-selective Living Polymerization of <Emphasis Type="Italic">rac</Emphasis>-Phenyl Isocyanide Using Chiral Palladium Catalyst

We report the polymerization of phenyl isocyanides with the chiral palladium(II) initiating system. The resulting polymers with optically active properties were obtained by polymerization of the racemic isocyanide monomer (rac-1), and enantiomerically unbalanced polymerization of the monomer was found, providing substantial evidence for the enantiomer-selective polymerization of rac-1 mediated through chiral catalyst. A comparison between the enantiomerically pure monomers, 4-isocyanobenzoyl-L-alanine decyl ester (1s) and 4-isocyanobenzoyl-D-alanine decyl ester (1r), revealed a drastic discrepancy in the reactivity ratio of their homopolymerizations. It turned out that the monomer reactivity ratio of 1s was higher than that of 1r with chiral ligands. The results clearly demonstrated the inclination for incorporation of the 1s enantiomer during the polymerization process and thus resulted in the enantiomer-selective polymerization in this system. The effects of the catalyst chirality on the optically active properties of polymerization were investigated, and it was concluded that the formation of higher-ordered conformation with a handed helicity might be attributed to the chiral induction of chiral palladium(II) catalyst. Moreover, the polymers obtained through the enantiomer-selective polymerization of the enantiomerically pure monomer were with a significant improvement of the optical activity if the chirality of the monomer and the catalyst matched with each other.     

Asymmetric polymerization of methacrylates

The syntheses of optically active polymers having helical conformation from bulky methacrylates are reviewed focusing on selected topics. The monomers include triphenylmethyl methacrylate and its analogues. Asymmetric anionic polymerization of the monomers gives isotactic, optically active polymers having a helical structure with excess helicity. The isotactic content and the extent of helical‐sense excess depend on the monomer structure and the reaction conditions. In the case of methacrylates, completely isotactic and single‐handed helical polymers can be produced by asymmetric anionic polymerization (helix‐sense‐selective polymerization). Asymmetric radical polymerization is also possible for this class of monomer. Some of the helical polymers show chiral recognition ability toward a wide range of racemic compounds. Polymers having main‐chain configurational chirality are also discussed.     

Palladium-catalyzed diastereoselective coupling of propargylic oxiranes with terminal alkynes

[reaction: see text] A diastereoselective coupling of propargylic oxiranes with terminal alkynes has been developed with use of a palladium catalyst. The stereochemistries of the resulting 4-alkynyl-substituted 2,3-allenols have been altered depending on the palladium catalyst. An optically active anti-substituted allene was synthesized from the reaction of an enantiomerically enriched propargylic oxirane without loss of chirality.     

Living and enantiomer-selective polymerization of allene initiated by Ni complex containing chiral phosphine

In the polymerization of chiral allene by using chiral phosphine complex, the polymerization rate of L-1 is approximately 1.9 times that of D-1. This catalyst has enantiomer-selectivity for the polymerization of chiral allene derivative monomer.     

(−)-Sparteine: The compound that most significantly influenced my research

A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004     

Biaryl-based macrocyclic and polymeric chiral (salophen)Ni(II) complexes: synthesis and spectroscopic study.

Polymeric/oligomeric and macrocyclic (salophen)Ni(II) complexes have been synthesized starting from both an achiral biphenol dialdehyde and an optically active BINOL dialdehyde. It was found that these polysalophens contain nonplanar coordination of Ni(II) units that are paramagnetic. This is different from the previously reported (salophen)Ni(II) complexes which are square planar and diamagnetic. The nonplanar (salophen)Ni(II) units make the new polymeric Ni(II) complexes different from the helical structure proposed for chiral biaryl-based polymers containing square-planar (salophen)Ni(II) units. The copolymerization of the chiral binaphthyl monomer with the achiral biphenyl monomer demonstrates that the chirality of the binaphthyl unit is not propagated along the biphenyl polymer chain.     

Stereospecific polymerization and chiral initiation,chiral crystallization and chiral nucleation

Helical macromolecules which are configurationally and conformationally specific can now be synthesized. Monomer structures must be selected that demand spacial restriction for monomer addition. High specificity of monomer addition during polymerization has parallels in crystallization of some inorganic salts from aqueous solution. Initiation of highly specific polymerizations with chiral initiators give helical polymers with substantial one-handedness. Nucleation of certain inorganic salts with chiral nucleating agents, the enantiomers of the salts produce enantiomerically pure chiral salts.     

SYNTHESIS, CHARACTERIZATION OF CHIRAL POLY（ESTER AMIDE）S DERIVED FROM L-ISOLEUCINE

A series of new optically active aromatic poly(ester arnide)s containing a chiral group in the side chain prepared from the p-toluenesulfonic acid salt of o,o‘-bis(leucyl)-hexanediol (TS^- LHD^ TS^-) and p-phthaloyl chloride and styrene-2,5-dicarbonyl chloride styrene have been synthesized by interfacial polymerization. The structure of the monomer is elucidated by FT-IR and elemental analysis. The thermal properties of the polymers were studied by DSC and TGA. The chiroptical properties of the above polymer have also been studied by circular dichroism (CD) spectroscopy. Results indicated that these polymers form helical structures.     

Enantioseparation of doubly functionalized polar norbornenes by HPLC and their ruthenium‐catalyzed ring‐opening metathesis polymerization

Doubly fuctionalized polar norbornenes bearing the cyano and ester groups in 2,3‐positions are synthesized and enantiomers are separated by high performance liquid chromatography (HPLC) with a chiral stationary phase. These optically active monomers are polymerized by ruthenium carbene catalysts, and high yields of the polymers were obtained. The chiral monomer bearing ethyl ester gave an optically active polymer of lower, but opposite sign of optical rotation (monomer [α]_D = +61.0°, polymer [α]_D = ?3.1°). The circular dichroism (CD) of the obtained chiral polymers gave a Cotton effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 485–491, 2010     

Polymerization of optically active 2-fluorophenyl-4-fluorophenyl-2-pyridylmethyl methacrylate with anionic and radical initiators: Stereospecificity and helix-sense selection

Almost optically pure (+)- and (−)-2-fluorophenyl-4-fluorophenyl-2-pyridylmethyl methacrylate (2F4F2PyMA) monomers were obtained by HPLC resolution of the racemic monomer and polymerized with the use of anionic and free-radical initiators. Helix-sense selectivity during the polymerization seemed to be governed mainly by the chirality of the monomer itself, and the polymers obtained by using the complex of N,N′-diphenylethylenediamine monolithium amide with (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP) in toluene at −78°C appeared to possess single-handed helical conformation (+)-poly[(−)-2F4F2PyMA], [α]₃₆₅ + 1510°; (−)-poly[(+)-2F4F2PyMA], [α]₃₆₅ − 1610°]. The single-handed helical (+)-poly[(−)-2F4F2PyMA] and (−)-poly[(+)-2F4F2PyMA] obtained with the PMP complex exhibited better chiral recognition ability toward trans-stilbene oxide compared with the single-handed helical poly(rac-2F4F2PyMA) prepared previously. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2645–2648, 1999     

Isolation of stable enantiomerically pure telluroxides and their stereochemistry

Optical resolution of kinetically and thermodynamically stabilized diaryl telluroxides possessing bulky substituents (rac-1a-d) and amino group (rac-2a-c), respectively, by liquid chromatography using optically active columns yielded stable enantiomerically pure telluroxides. The absolute configurations of the optically active telluroxides were determined by comparing their specific rotations and CD spectra with those of sulfur or selenium analogues. The kinetics for the racemization of optically active telluroxides in solution was studied, and it was found that kinetic and thermodynamic stabilization were very effective preventing the racemization of telluroxides. The stabilization energy of telluroxides by intramolecular coordination of the amino group to the tellurium atom was estimated to be ca. 5 kcal mol-1 by variable temperature 1H NMR measurement. The mechanism for the racemization of optically active telluroxides was studied by an isotope experiment using H2(18)O, and the results indicated that optically active telluroxides underwent racemization via an achiral tetracoordinated hydrate.     

Asymmetric selective polymerization of racemic 1,2-diphenylethyl methacrylate with the ethylmagnesium bromide-(−)-sparteine complex

Asymmetric selective (or stereoelective) polymerization of racemic 1,2-diphenylethyl methacrylate (DPEMA) with ethylmagnesium bromide (EtMgBr)-(?)-sparteine catalyst was studied in toluene at ?78°C. In the polymerization (S) enantiomer was consumed preferentially and the enantiomeric excess of initially polymerized (S) enantiomer was consumed preferentially and the enantiomeric excess of initially polymerized DPEMA was greater than 90%. Optically pure (R) monomer was recovered at about 70% polymer yield. Poly(DPEMA) obtained with EtMgBr-(?)-sparteine complex was highly isotactic. It was found in the polymerization of optically active DPEMA that optical rotation of poly(DPEMA) was dependent on the tacticity and that isotactic and syndiotactic poly(DPEMA)s showed opposite optical rotations. Circular dichroism spectra of the optically active polymers were measured.     

Polymerization of an optically active phenylacetylene derivative bearing an azide residue by click reaction and reaction with a rhodium catalyst

A facile method for synthesizing diverse optically active polymers with different backbone structures was developed by the polymerization of an optically active aromatic azide bearing an acetylene unit with a rhodium catalyst followed by the click reaction of the pendant azides or by the click polymerization of the monomer.     

L-丙烯酸薄荷酯与2,5-二(4'-己氧基苯基)苯乙烯无规共聚物的合成和旋光性质

通过自由基共聚合制备了一系列L-丙烯酸薄荷酯( L-MtA)与2,5-二(4'-己氧基苯基)苯乙烯(BHPSt)的共聚物L-MtA(x)-co-BHPSt(1-x).利用UV-Vis和1H-NMR光谱表征了共聚物的组成,根据Kelen-Tüd(o)s (K-T)方法计算得到的L-MtA和BHPSt的竞聚率分别为0.36...     

Diastereoselective Hartwig-Buchwald reaction of chiral amines with rac-[2.2]paracyclophane derivatives

A Hartwig-Buchwald addition of a variety of chiral amines to rac-4-bromo-[2.2]paracyclophane and rac-trifluoromethanesulfonic acid (4-[2.2]paracyclophane) ester was performed with high diastereoselectivities. Kinetic racemic resolution of the starting materials was achieved, providing a rapid access to enantiomerically enriched 4-bromo-[2.2]paracyclophane and the corresponding enantiomerically pure [2.2]paracyclophane amines. Additionally, the first reaction of a secondary amine with a [2.2]paracyclophane halide was achieved.     

Helical chirality of π‐conjugated main‐chain induced by polymerization of phenylacetylene with chiral bulky pinanyl groups: Effects of the flexible spacer and polymerization catalyst

Three optically active phenylacetylene polymers with chiral bulky pinanyl groups, (?)‐poly[4‐(dimethylpinanylsilyl)phenylacetylene] [(?)‐poly(PSPA)], (+)‐poly{4‐[3‐(10‐pinanyl)tetramethyldisiloxy]phenylacethylene} [(+)‐poly(PDSPA)], and their copolymer [(?)‐copoly(PSPA/PDSPA)], were synthesized. We observed high chirality in the main‐chain chromophore of (?)‐poly(PSPA), due to the presence of a chiral helix, with circular dichroism spectroscopy. In contrast, (+)‐poly(PDSPA),with flexible SiOSi spacers between the chiral pinanyl group and the main chain, had lower chirality. (?)‐Poly(PSPA), with large circular dichroism signals, was prepared by polymerization with a rhodium catalyst and had a highly stereoregular main chain (high cis‐configuration percentage). However, (?)‐poly(PSPA) prepared with a tungsten catalyst had lower chirality and lower stereoregularity in the main chain. A membrane from (?)‐poly(PSPA) showed enantioselective permeability for tryptophan in an aqueous solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1689–1697, 2002     

Preparation of optically active poly-β-propiolactones—II. Preparation of optically active poly-α-methyl-α-ethyl-β-propiolactones

Optically active poly-α-methyl-α-ethyl-β-propiolactones were prepared by stereoelective polymerization of the racemic monomer and by anionic polymerization of optically active monomers. Important differences in properties were observed between racemic and optically pure polymers, the latter having a much higher melting point. Chiroptical and structural studies of polymers of different enantiomeric composition are reported.     

Stereospecific Polymerization and Chiral Crystallization

Configurationally and conformationally specific polymerization processes which lead to helical macromolecules can be successfully carried out when monomer structure, polymerization mechanism, and spatial restrictions for monomer addition are all carefully considered. Under certain conditions, optically active polymers having a single helical screw sense can be prepared. Surprisingly, the chiral crystallization of certain inorganic salts has much in common with stereospecific polymerization mentioned above. Achiral sodium chlorate and sodium bromate can crystallize spontaneously from aqueous solutions to give a mixture of pure levorotatory and pure dextrorotatory isotropic crystals. The crystallization of these salts can also be nucleated with traces of levo- or dextro- rotatory crystals to furnish new crystals with a high degree of chiroptical purity. Our varied efforts within the confines of these two related fields are summarized.     

Palladium-catalyzed regio- and stereoselective formate reduction of fluorine-containing allylic mesylates. A new entry for the construction of a tertiary carbon attached with a fluoroalkyl group

The regioselective palladium-catalyzed formate reduction of gamma-fluoroalkylated allylic esters is described. Reduction of the allylic esters under the influence of palladium with a monodentate phosphine ligand proceeded preferentially at the gamma position, the corresponding reduction products with a fluoroalkyl group at the tertiary carbon being afforded in high yields. When the chiral allylic ester was employed, complete chirality transfer was observed, leading to the optically active materials in high yields.     

Synthesis of poly(vinyl alcohol) containing asymmetric nucleic acid base derivatives as grafted pendants

The preparations of new model polymers of polynucleotides with linear poly(vinyl alcohol) (PVA) backbones and an optically active nucleic acid base derivative as a pending side chain are described. (±)-, (+)-, and (?)-2-(thymin-1-yl)propionic acid were grafted onto PVA through ester bonds by direct coupling with dicyclohexylcarbodiimide (DCC) in the presence of highly active catalyst 4-pyrrolidinopyridine (PPY) to give optically active graft polymers. The corresponding monomer and dimer models have been prepared.