Asymmetric induction copolymerization of optically active l-menthyl vinyl ether with styrene and N-phenylmaleimide

The copolymerizations of l-menthyl vinyl ether (l-MVE) with styrene (St) and N-phenylmaleimide (N-PMI) as comonomers were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to give optically active copolymers. After the removal of the optically active menthyl group by use of hydrogen bromide gas, the ether-cloven l-MVE-N-PMI copolymer (VA-N-PMI) was still optically active. On the other hand, the optical activity of l-MVE-St copolymer disappeared after ether cleavage. It is thought that asymmetric induction took place in the polymer main chains. The optical rotatory dispersion and circular dichroism of the original and ether-cloven copolymers were measured in order to confirm the asymmetric induction.     

Asymmetric induction radical copolymerization of optically active l-menthyl vinyl ether with vinylene carbonate and indene

The copolymerizations of l-menthyl vinyl ether (l-MVE) with the monomers vinylene carbonate (VCA) and indene (IN) were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to obtain optically active copolymers. The optically active l-menthyl residue from the copolymer main chain was removed using dry hydrogen bromide gas. After the ether cleavage reaction, the copolymers prepared (VA–VCA and VA–IN) were still optically active, and hence it was found that asymmetric induction had taken place in the copolymer main chain. The optical rotatory dispersion (ORD) and circular dichroism (CD) data of the original and ether-cloven copolymers were also determined.     

Radical copolymerization of optically active l-menthyl vinyl ether with maleic anhydride,dimethyl maleate,and dimethyl fumarate

The copolymerizations of l-menthyl vinyl ether (l-MVE) with the monomers, that is, maleic anhydride (MAn), dimethyl maleate (DMM), and dimethyl fumarate (DMFu), were undertaken to obtain optically active copolymers. The optically active l-menthyl group in the side chain of copolymers was removed by the ether cleavage reaction with dry-hydrogen bromide gas. The ethercloven copolymers were still optically active. Hence it was concluded that asymmetric carbon atoms were introduced into the copolymer main chain, the reason given being that l-MVE and comonomers (MAn, DMM, and DMFu) made the stereoselective charge-transfer complex one another and copolymerized stereospecifically. From the results of the measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) for copolymers before and after the ether cleavage reaction, the mode of bond opening for α,β-substituted monomers (MAn, DMM, and DMFu) was discussed and the microstructures of copolymers were prepared.     

Effect of catalysts on asymmetric induction cationic copolymerization of l-menthyl vinyl ether with indene

Cationic copolymerization of l-menthyl vinyl ether (l-MVE) with indene (IN) was carried out with several catalysts in toluene (Tol) at 0°C. The catalysts used were BF₃OEt₂, CH₃COClO₄, and SnCl₄. l-Menthyl residue, an optically active side chain of the copolymer obtained, was removed with dry hydrogen bromide gas by the ether cleavage reaction. Ether-cloven copolymers [vinyl alcohol(VA)–IN] also had optical rotation. The efficiency of asymmetric induction to the polymer main chain was in the order of BF₃OEt₂ > CH₃COClO₄ > SnCl₄.     

The effect of solvents on asymmetric induction cationic copolymerization of l-menthyl vinyl ether with indene

Cationic copolymerization of l-menthyl vinyl ether (l-MVE) with indene (IN) was carried out in several solvents with BF₃OEt₂ as catalyst at 0°C. The solvents used in this study were selected toluene (Tol), chloroform (CHCl₃), chlorobenzene (BzCl), 1,2-dichloroethane (EtCl₂), and nitrobenzene; (BzNO₂)/Tol = 65/35 mixture solvent. l-Methyl residue, which is an optically active side chain of copolymer produced by cationic copolymerization, was removed with dry hydrogen bromide gas by ether cleavage reaction. The copolymer [vinyl alcohol(VA)–lN], produced by the ether cleavage reaction, also showed optical rotation. From this result, therefore, it was concluded that asymmetric induction takes place in the copolymer main chain. The efficiency of asymmetric induction was determined by the measurement of optical rotation of VA–IN copolymer after the ether cleavage reaction. The efficiency of asymmetric induction in the copolymer main chain developed from the variation on polymerization solvents; the order was Tol > EtCl₂ > BzCl > CHCl₃ > BzNO₂/Tol (65/35) mixture solvent.     

Asymmetric radical copolymerization of S(−)-α-phenethylammonium butadiene 1-carboxylate with styrene

Radical copolymerization of S(?)-α-phenethylammonium butadiene 1-carboxylate (S-PBu) with styrene was performed in methanol, using azo-bis-isobutyronitrile as initiator. It was confirmed that the copolymers had trans 1,4 units of S-PBu; the copolymers after removal of chiral side chain were optically active. From CD spectra of the copolymers after removal of chiral amine from the side chain, it was found that the asymmetric induction occurred in the copolymer main chain. The copolymerization parameters of S-PBu were determined and are discussed.     

Asymmetric Induction Copolymerization of Optically Active N-(1-Menthyl Carboxylatomethyl) Citraconimide with Methyl Methacrylate

Copolymerization of an optically active N-(1-menthyl carboxylatomethyl)citraconimide (MCMCI) was carried out with methyl methacrylate (MMA) with azobisisobutyronitrile as the initiator in benzene at 50°C. All the copolymers obtained were optically active. After the removal of the optically active menthyl group, the hydrolyzed poly(MCMCI-co-MMA)'s still showed optical activity. The asymmetric induction to the copolymer main chain and the mechanism are discussed based on the measurements of optical rotatory dispersion and circular dichroism of the original and hydrolyzed copolymers.     

Asymmetric Syntheses XXVI: Catalytic Enantioselective Syntheses of β-Hydroxy Esters via Double Chiral Induction in Asymmetric Reformatsky Reactions

Catalytic asymmetric Reformatsky reactions of benzaldehyde with optically active menthyl bromoacetates in the presence of Zn-Cu couple were performed using 0.25 equiv. of (1R,2S) or (1S,2R)-dimethyl-2-amino-1,2-diphenyl ethanol as chiral ligand to obtain β - hydroxy esters with enantioselectivities up to 60.2%. The obvious double chiral induction effect was observed while chiral ligands matched with optically active substrates.     

Optically active vinyl polymers containing fluorescent groups—7: The distribution of monomeric units in cationically prepared copolymers of 9-vinylcarbazole and (−)menthyl vinyl ether

u.v. Absorption, ¹H-NMR, fluorescence emission and circular dichroism spectra together show clearly that stereoregular copolymers obtained cationically from 9-vinylcarbazole and (?)menthyl vinyl ether have significant block-like character. In contrast to results for related optically active copolymers, plots of circular dichroism absorption intensity versus copolymer composition exhibit a pronounced maximum corresponding to a molar composition 20% 9-vinylcarbazole, 80% (?)menthyl vinyl ether. This maximum does not correspond, as expected, with the presence of isolated carbazole units in a chiral polymer environment.     

Preparation,characterization, and chiral recognition of optically active polymers containing pendent chiral units via reversible addition‐fragmentation chain transfer polymerization

Optically active polymers bearing chiral units at the side chain were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization in the presence of 2,2′‐azobisisobutyronitrile (AIBN)/benzyl dithiobenzoate (BDB), using a synthesized 6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose (VBPG) as the monomer. The experimental results suggested that the polymerization of the monomer proceeded in a living fashion, providing chiral group polymers with narrow molecular weight distributions. The optically active nature of the obtained poly (6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose) (PVBPG) was studied by investigating the dependence of specific rotation on the molecular weight of PVBPG and the concentration of PVBPG in tetrahydrofuran (THF). The results showed the specific rotation of PVBPG increased greatly with the decrease of the concentration of the PVBPG homopolymer. In addition, the effect of block copolymers of PVBPG on the optically active nature was also investigated by preparing a series of diblock copolymers of poly(methyl methacrylate) (PMMA)‐b‐PVBPG, polystyrene (PS)‐b‐PVBPG, and poly(methyl acrylate) (PMA)‐b‐PVBPG. It was found that both the homopolymer and the diblock copolymers possessed specific rotations. Finally, the ability of chiral recognition of the PVBPG homopolymer was investigated via an enantiomer‐selective adsorption experiment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3788–3797, 2007     

接枝于聚薄荷基丙烯醇的手性氨基醇的合成及其对Henry反应的不对称催化作用的研究

一种新型的旋光活性的氨基醇类聚合物被合成出来。以旋光活性聚薄荷基乙烯基酮为原料, 将聚薄荷基乙烯基酮用氢化铝锂还原后得到聚薄荷基丙烯醇(poly-MPO),poly-MPO与氢化钠反应后与环氧氯丙烷反应得到固载环氧丙烷的poly-MPO。将固载环氧丙烷的poly-MPO与各种类型的胺反应得到接枝于聚薄荷基丙烯醇的手性氨基醇(poly-MPO)-APO。将其应用在催化不对称Henry反应中得到了高产率、中等选择性的产物。     

Helix‐sense‐selective copolymerization of triphenylmethyl methacrylate with chiral 2‐isopropenyl‐4‐phenyl‐2‐oxazoline

The asymmetric induction leading to a one‐handed helix was investigated in the anionic and radical copolymerization of triphenylmethyl methacrylate (TrMA) and (S)‐2‐isopropenyl‐4‐phenyl‐2‐oxazoline ((S)‐IPO), and highly isotactic copolymers with a reasonable optical activity were obtained. In the anionic copolymerization, the optical activity of the obtained copolymers depended on the polarity of solvents, and a highly optically active copolymer was produced in the copolymerization in toluene. The chiral oxazoline monomer functioned not only as a comonomer but also as a chiral ligand to endow the polymer with large negative optical rotation in the copolymerization with TrMA. The copolymers with small positive optical rotation were obtained in THF, indicating that IPO unit may work only as the chiral monomer that dictates the helical sense via copolymerization with TrMA. The isotacticity of the obtained copolymers depended on the contents of TrMA units in the copolymers, but was almost independent of the solvent for copolymerization. In the radical copolymerization, the obtained copolymers exhibited small optical activities. It seemed that the chiral monomer cannot induce one‐handed helical structure of TrMA sequences even if the sequences probably have a high isotacticity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 441–447     

Asymmetric selective copolymerization of propylene oxide with d-camphoric acid anhydride

The ring-opening copolymerization of propylene oxide with d-camphoric acid anhydride [α]_D ?3.4° was carried out with diethylzinc and triethylamine as catalysts. It was found that the products were alternating copolymers which were optically active. The optical rotatory dispersion curves were found to fit a simple Drude equation having a λ_c value of 201 mμ. The specific rotation increased with increasing intrinsic viscosity of the product. The propylene oxide recovered from the polymerization system was optically active. Its specific rotation increased with increasing polymerization time. It is thought that the asymmetric selective copolymerization of propylene oxide is caused by the influence of the optically active camphoryl group of the polymer end.     

Editorial

Abstract

Asymmetric syntheses of optically active polymethacrylate, polyacrylate, polyacrylamide, and polyisocyanate with helical conformation and their chiral recognition abilities are described. 1-Phenyldibenzosuberyl methacrylate (PDBSMA) gave a purely onehanded-helical, optically active polymer ([α]₃₆₅ +1670 ～ +1780º) with almost perfectly isotactic structure by anionic polymerization using optically active initiators. Radical polymerizations of PDBSMA using chiral initiators, chain transfer agents, and additives also afforded optically active polymers with a prevailing onehanded helicity. Triphenylmethyl acrylate yielded an optically active, helical polymer ([α]₃₆₅ +102º) having a dyad isotacticity of 70% using an optically active anionic initiator. Although the polyacrylate demonstrated chiral recognition ability as a chiral stationary phase for HPLC, the ability was low mainly because of the low degree of one-handedness. N-(3-Chlorophenyl)-N-phenylacrylamide gave an optically active, helical polymer ([α]_365–343º) in the asymmetric anionic polymerization; the polymer had a dyad tacticity of 77%. Optically active polyisocyanates with a predominantly one-handed helical conformation were prepared in homo-and co-polymerization of optically active phenyl isocyanate derivative. These polyisocyanates showed the ability to discriminate enantiomers in solution.     

Main-Chain Chirality and Optical Activity in Polymers Consisting of C?C Chains

Main-chain chirality is the optical activity resulting from the configurational or conformational arrangement in the main chain of a polymer. The chirality of the most important types of structures has been investigated on the basis of systematic considerations of symmetry. This has led to the surprising result that even in polymers derived from 1-substituted or nonsymmetric 1,1-disubstituted olefins (the technologically most important polymers) several types of chiral structures exist, which are expected to result in optical activity if a particular enantiomer is favorably formed. By carrying out an asymmetric cyclopolymerization, it has been possible to obtain certain structural types in the form of optically active copolymers or homopolymers (e.g., copolymers of styrene with methyl methacrylate, or even the homopolymer of styrene). Another new group of optically active polymers consists of the atropisomeric helical polyisocyanides, poly(trityl methacrylates), and polychlorals. Optically active polymers are already used as adsorbents for the chromatographic separation of racemic mixtures. Further applications are likely to emerge.     

Asymmetric Photochemical Synthesis of Chiral 5‐(R)‐(l)‐Menthyloxy‐4‐Cycloaminobutyrolactones

Through photocatalysed regiospecific and stereoselective additions of cycloamines to 5‐(R)‐(l)‐menthyloxy‐2 (5H)‐furanone (3), chiral 5‐(R)‐(l)‐menthyloxy‐4‐cycloaminobutyrolactones were synthesized. In the new asymmetric photoaddition of compound 3, the N‐methyl cyclic amines (4) gave novel chiral C? C photoadducts (5) in 24–50% isolated yields with d. e. ≥ 98%. However, the secondary cyclic amines (6) afforded optically active N? C photoadducts (7) in 34–58% isolated yields with d. e. ≥ 98% under the same condition. All the synthesized optically active compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]₅₈₉²⁰, IR, ¹H NMR, ¹³C NMR, MS and elementary analysis. The photosynthesis of chiral butyrolactones and its mechanism were discussed in detail.     

Well‐defined amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chains

A series of well‐defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(vinyl acetate) (PVAc) side chains were synthesized via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization followed by selective hydrolysis of poly(tert‐butyl acrylate) backbone. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromopropanoyloxy)methyl) acrylate, was first prepared, which can be polymerized via RAFT in a controlled way to obtain a well‐defined homopolymer with narrow molecular weight distribution (M_w/M_n = 1.08). This homopolymer was transformed into xanthate‐functionalized macromolecular chain transfer agent by reacting with o‐ethyl xanthic acid potassium salt. Grafting‐from strategy was employed to synthesize PtBA‐g‐PVAc well‐defined graft copolymers with narrow molecular weight distributions (M_w/M_n < 1.40) via RAFT of vinyl acetate using macromolecular chain transfer agent. The final PAA‐g‐PVAc amphiphilic graft copolymers were obtained by selective acidic hydrolysis of PtBA backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media were determined by fluorescence probe technique. The micelle morphologies were found to be spheres. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6032–6043, 2009     

Synthesis of chiral micelles and nanoparticles from amino acid based monomers using RAFT polymerization

Homopolymers of ^tbutyl acrylate (P^tBuA) and a monosubstituted acrylamide (PAM) having an amino acid moiety in the side chain, N‐acryloyl‐(L )‐phenylalanine methyl ester 1 , have been synthesized by Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization. Diblock copolymers of these homopolymers were also synthesized by chain extending P^tBuA with monomer 1 and after modification, using simple acid deprotection chemistries of the acrylate block to afford a poly (acrylic acid) block, an optically active amphiphilic diblock copolymer was isolated. The optically active amphiphilic diblock copolymers, which contain chiral amino acid moieties within the hydrophobic segment, were then self‐assembled to afford spherical micelles which were subsequently crosslinked throughout the shell layer to afford robust chiral nanoparticles. The hydrodynamic diameters (D_h) of the block copolymer micelles and nanoparticles were measured by dynamic light scattering (DLS) and the dimensions of the nanoparticles were determined using tapping‐mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3690–3702, 2008     

Novel Synthesis of Optically Active 2‐Ethylhexanoic Acid, 2‐Ethylhexanol,and 2‐Ethylhexylamine via the Asymmetric Favorskii Rearrangement

The asymmetric Favorskii rearrangement of optically active α‐haloketones, which are easily prepared from chiral menthyl‐4‐toluenesulfoxide in several steps using primary or secondary amines, yields their corresponding secondary or tertiary chiral amides. The secondary chiral amides were converted to acids or amines using acylation followed by hydrolysis or reduction. In addition, the tertiary amides were directly reduced to alcohol with Super‐Hydride^®.     

Asymmetric cyclopalladation in the ferrocene series as a tool for enantioselective synthesis. Preparation of some analogues of natural products

The previously described asymmetric cyclopalladation has been applied to the esters of 7-dimethylamino-7-ferrocenylenanthic acid, I, to afford the optically active palladium derivative, II. The absolute configuration of the chiral plane is determined by the configuration of the inductor: the acylamino acid salt. The palladium atom in II was then substituted by a σ-ketovinyl group using the reaction with pentyl vinyl ketone, to yield III. The latter substance undergoes full reduction when treated with Et₃SiH + CF₃COOH (the ionic hydrogenation reaction) resulting in the optically active prostanoic acid analogue, IV. On the other hand, III in the form of the methiodide is reduced by NaBH₄ with the elimination of the amine group and the and the formation of allyl alcohol V. This kind of side chain is characteristic of many prostaglandins. Bromination of II followed by the repeated cyclopalladation opens the way to trisubstitute derivatives. The pathway outlined provides a rapid synthesis of optically active compounds which are the ferrocene analogues of natural prostaglandins.