Synthesis of chiral polymers containing the acetoxybornyl group and their applications on the asymmetric induction

Optically active 2-endo-actoxy-5-endo-bornyl methacrylate (ABMA) was prepared from (+)-camphor. The homopolymerization of ABMA and copolymerization of ABMA with achiral methyl methacrylate (MMA) or styrene (St) were carried out with 2,2′-azobisisobutyronitrile (AIBN) in benzene. Effects of temperature, solvents, and reaction time on the copolymerization were discussed. The monomer reactivity ratios(r₁, r₂) for poly(ABMA-co-MMA) and poly(ABMA-co-St) and Q and e values for the chiral ABMA in the copolymerization systems were evaluated by the Fineman—Ross method. The absolute value of the specific rotation of poly(ABMA-co-MMA) increased with increasing ABMA unit content. A small deviation from linearity was observed, which suggests that asymmetry is not introduced into the copolymer main chain. Temperature and solvent effects on the specific rotation of the chiral homopolymer and copolymers were investigated. The results suggest that the chiral polymers synthesized in this investigation did not show a strong preference for a particular helical conformation. Applications of the chiral polymers on the asymmetric addition of n-butyllithium to aldehydes were also discussed.     

Synthesis and characteristics of chiral polymers with camphanediol moieties

Optically active exo,exo-2,3-camphanediol (CPO) was synthesized from (+)-camphor. The chiral polymers poly(CPO-co-TDI) and poly(CPO-co-IPDI) were synthesized by step polymerization of chiral compound CPO with toluene-2,4-diisocyanate (TDI) and isophorone diisocyanate (IPDI). Effects of solvents, reaction time and temperature on the polymerization were investigated. To investigate the stereo structure of the chiral polymers, two kinds of model compounds, exo-exo-2,3-bornylene N,N′-diphenyldicarbamate and exo,exo-2,3-bornylene N,N′-dipropyldicarbamate, related to the prepared polymers were synthesized. Chiroptical characteristics and stereo structures of the chiral polymers were investigated by using a circular dichroic spectrometer. Effects of temperature and solvents on the specific rotation of the chiral polymers were evaluated. The results obtained in this investigation suggest that the synthesized chiral polymers have no one-handed helix conformation.     

Characterization of Thermally Stable AB-type Poly(ether-amide)s Derived from AB-type Monomers by Fluoro Displacement Reaction

Two AB-type monomers 4-fluoro -N-(4-(2-(4-hydroxyphenyl) propan-2-yl) phenyl) benzamide and 4-fluoro -N-(5-hydroxy naphthyl) benzamide were synthesized. The AB-type poly(ether-amide)s (PEAs) were derived by self-polymerization via the nucleophilic aromatic displacement reaction of AB-type monomers. The structure of AB-type monomers and PEAs were confirmed by FT-IR and H¹-NMR spectroscopy. The PEAs were characterized by TGA, DSC, XRD, solution viscosity and solubility. X-ray diffraction studies indicated that the poly (ether-amide)s were amorphous. Poly(ether-amide)s exhibited excellent thermal stability and solubility. All the PEAs were readily soluble at room temperature in polar aprotic solvent DMSO, NMP and DMAc and also in less polar solvents such as m-cresol and pyridine.     

Highly Stereoselective Synthesis of Novel Multistereogenic Bis‐Bifunctional Ligands Based on [2.2]Paracyclophane‐ 4,7‐quinone,their Structure Elucidation and Application in Asymmetric Catalysis

Bis‐bifunctional cis‐4,7‐diarylsubstituted‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophanes 3–6 were synthesized by a highly diastereoselective reaction of ortho‐substituted aryllithium reagents with [2.2]paracyclophane‐4,7‐quinone ( 1 ). Enantiomerically pure diols 3–5 were tested as chiral inductors in the enantioselective addition of diethylzinc to benzaldehyde (up to 93.5% ee). Acid dehydration of cis‐4,7‐di(2‐methoxyphenyl)‐4,7‐dihydroxy‐4,7‐dihydro[2.2]paracyclophane ( 3 ) results in 4,7‐dihydro‐7,8‐di(2‐methoxyphenyl)[2.2]paracyclophane‐4‐one ( 8 ) – a planar chiral cyclohexadienone of the [2.2]paracyclophane series with a para‐semiquinoid substructure. X‐Ray investigations of compounds 3, 4 and 8 were performed.     

Enantioface differentiation by using soluble chiral polymers having 2,3-exo-bornanediol groups

Soluble linear polymers containing 2,3-exo-dihydroxy-3-endo-p-tolyl-3-bornyl groups prepared by reaction of lithiated linear polystyrenes with (-)-2-exo-hydroxy-3-bornanone, are treated with lithium aluminium hydride to form complexes which can be used as reducing reagents. The highest enantioselectivity compared with those cases using crosslinked polystyrene as carrier and chiral low molecular weight compounds is achieved by linear polystyrene having chiral groups. The advantages of soluble polymer-bound chiral reagents are discussed. The effect of alcohols, the reaction temperature, the sort of solvents, and the molar ratio of the reagent to ketone on the asymmetric reduction is also discussed.     

Photoresponsive Functionalized Vinyl Cinnamate Polymers: Synthesis and Characterization

A series of functionalized vinyl cinnamate monomers were synthesized by the reaction of hydroxyethylmethacrylate and various substituted cinnamoyl chlorides. Electron donating and accepting functional groups such as −OCH₃, −Cl and −NO₂ were introduced at the para position of cinnamoyl chloride. Homopolymerization of the synthesized monomers were carried out in dimethylformamide using azobisisobutyronitrile as a free radical initiator at 80°C for 12h. The structures of the synthesized monomers and their polymers were characterized using Fourier transform infrared (FTIR), ¹H and ¹³C nuclear magnetic resonance spectroscopic techniques. Solid-state crosslinking of the above photosensitive polymers was studied by UV and FTIR spectroscopic techniques. The effects of various functional groups and the addition of sensitizer (benzophenone) on the photocrosslinking nature of the polymers were studied. The mechanism of photocrosslinking is a (2+2)π electron cycloaddition and not cis–trans isomerization in the functionalized polyvinylcinnamates. © 1997 SCI     

Novel atropisomeric binaphthol containing comb-shaped copolymers forming chiral nematic phases

Novel comb-shaped liquid crystalline acrylic copolymers consisting of nematogenic methoxy-phenylbenzoate acrylic monomers (A) together with novel chiral binaphthol (BN) methacrylic monomers (MB-m) were synthesized in this study. The prepared copolymers differ in spacer lengths of MB-m (m = 3, 5, 11) and in their compositions. The homopolymers of the three new chiral BN monomers MB-m were also prepared. Copolymers with a low concentration of BN monomeric units (less than 16 mol %) display a cholesteric mesophase. The induced chirality in the polymers is due to atropisomerism (chirality due to hindered rotation around single bonds) of the BN molecules. The helical twisting power β (HTP) caused by the atropisomeric units in the synthesized copolymers was shown to decrease significantly on heating. The unusually high negative temperature coefficient of HTP observed above the glass transition temperature (T_g) could be explained in terms of conformational changes of the BN molecules in the copolymers.     

Preparation and Characterization of Polymer-dispersed Liquid Crystal Films Using Poly(bornyl methacrylate)

Chiral (+)-bornyl methacrylate and achiral (±)-bornyl methacrylate were synthesized from (+)-camphor and (±)-camphor, respectively. To investigate the influence of the steric environment of the chiral polymers on the electro-optical characteristics of polymer-dispersed liquid crystal (PDLC) films, a commercially available positive nematic liquid crystal E7 was dispersed in the chiral and achiral polymer matrices. The electro-optical characteristics and the microstructures of the PDLC films with chiral and achiral racemized polymers were investigated. It was found that PDLC films with chiral polymers have relatively high contrast ratio and fast falling speed, but there exists a transient damping response when a square pulse of 20ms and 60V is applied. Two distinct morphologies were observed: (1) a ‘continual channel’ with the chiral polymer matrix, and (2) an ‘isolated ball’ with the achiral racemized polymer matrix. The reversible turbid and transparent changes with an applied a.c. electric field were also investigated. © of SCI.     

Polymers containing sulfur in the side chain

We synthesized new thiodicarboxylic acids, p-tolylmethylthiomethylsuccinic acid and 1-naphthylmethylthiomethylsuccinic acid, and thiodiols, 2-(p-tolylmethylthiomethyl)-1,4-butanediol and 2-(1-naphthylmethylthiomethyl)-1,4-butanediol, by the addition of dimethyl itaconate with p-tolylmethanethiol or 1-naphthylmethanethiol, followed by hydrolysis or reduction, respectively, of the resultant dimethyl esters. These difunctional monomers were used for the synthesis of new linear polyesters and polyurethanes containing sulfur in the side chain. The polyesters were synthesized by melt polycondensation of the obtained acids with 2,2′-oxydiethanol. We found reduced viscosity, molecular weight (by GPC), and softening temperature for the reaction products. Low molecular weights, low softening temperature, and very good solubility in organic solvents are their characteristics. The polyurethanes were prepared by polyaddition diols with hexamethylene diisocyanate and tolylene diisocyanate in benzene. They were characterized by reduced viscosity and some tensile properties. The polyurethane derived from 2-(p-tolylmethylthiomethyl)-1,4-butanediol and hexamethylene diisocyanate (η_red. 1.17 dL/g) behaves like a high elasticity thermoplastic elastomer. Thermal stability of all polymers was determined by thermogravimetric analysis. The structure of the monomers and polymers were confirmed by elemental analysis and FTIR and ¹H-NMR spectroscopy. © 1996 John Wiley & Sons, Inc.     

Asymmetric transfer hydrogenation of prochiral ketone catalyzed over Fe-CS/SBA-15 catalyst

A heterogeneous chiral catalyst Fe(III)-CS (chitosan) complex/mesoporous molecular sieve SBA-15 (Santa Barbara Amorphous) was prepared. The asymmetric transfer hydrogenations of prochiral acetophenone and 4-methyl-2-pentanone to corresponding chiral alcohols were carried out on Fe-CS/SBA-15 at atmosphere pressure using 2-propanol as hydrogen donor. Effects of Fe content in catalyst, reaction temperature, reaction time and promoter KOH concentration on the conversion of substrates and enantio-selectivity were investigated. Fe-CS/SBA-15 with 2.2% mass fraction Fe exhibits considerable enantioselectivity and catalytic activity for the asymmetric transfer hydrogenations of aromatic ketone and aliphatic ketone. Under optimal reaction conditions: KOH concentration 0.03 mol/L, reaction temperature 70°C and reaction time 4 h, enantiomer excess (ee) of (R)-1-phenylethanol and conversion of acetophenone can reach 87.4% and 27.7%, respectively. Under the above KOH concentration and reaction temperature and reaction time of 8 h, the ee of (R)-4-methyl-2-pentanol and conversion 4-methyl-2-pentanone amounted to 50.2% and 25.5%, respectively. Translated from Petrochemical Technology, 2006, 35(9): 858–862 [译自: 石油化工]     

New optically active poly(amide-imide)s based on N,N′-(pyromellitoyl)-bis-L-amino acid and 1,3-bis(4-aminophenoxy) propane: Synthesis and characterization

Five new poly(amide-imide)s 8a–e were synthesized through the direct polycondensation reaction of five chiral N,N′-(pyromellitoyl)-bis-L -amino acids 3a–e with 1,3-bis(4-aminophenoxy) propane 7 in a medium consisting of N-methyl-2-pyrrolidone, triphenyl phosfite, calcium chloride, and pyridine. The polycondensation reaction produced a series of novel poly(amide-imide)s containing trimethylene moiety in the main chain in high yield with inherent viscosities between 0.34 and 0.65 dL/g. The resulted polymers were fully characterized by means of FTIR spectroscopy, elemental analyses, inherent viscosity, and solubility tests. Thermal properties of these polymers were investigated by using thermal gravimetric analysis (TGA) and differential thermal gravimetric (DTG). All of the polymers were soluble at room temperature in polar solvents such as N,N-dimethyl acetamide, N,N-dimethyl formamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. N,N′-(pyromellitoyl)-bis-L -amino acids 3a–e were prepared in quantitative yields by the condensation reaction of pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic acid 1,2,4,5-dianhydide) 1 with L -alanine 2a , L -valine 2b , L -leucine 2c , L -isoleucine 2d , and L -phenyl alanine 2e in acetic acid. Also 1,3-bis(4-aminophenoxy) propane 7 was synthesized by using a two-step reaction. At first 1,3-bis(4-nitrophenoxy) propane 6 was prepared from the reaction of 4-nitrophenol 4 with 1,3-dibromoprapane 5 in NaOH solution. Then, dinitro compound 6 was reduced by using Na₂S. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Functional monomers and polymers, 116. Asymmetric addition of n-butyllithium to aldehydes by chiral polymers and related compounds containing dimethylamino bornanol moieties

Asymmetric addition reaction of n-butyllithium to aldehydes was studied by using chiral polystyrene derivatives and chiral low molecular model compounds, both of which were derived from cis,endo-3-dimethylamino-2-hydroxybornane. The higher optical yields were achieved by using low molecular model compounds, and particularly the highest value was obtained in the case when ether was used as the solvent. The effect of reaction temperature, sort of the solvents and the molar ratio of the reagent to aldehyde on the asymmetric addition was also discussed.     

Synthesis and characterization of novel monomers and polymers containing chiral (−)-menthyl groups

To investigate the steric effects of chiral menthyl groups on the induction of cholesteric liquid crystals and the sensitivity of the photoisomerizable azobenzene derivatives, a series of chiral monomers and a photoisomerizable chiral azobenzene derivative with various spacers end-capped with (−)-menthyl group were synthesized. The structures of the novel chiral compounds synthesized in this investigation were identified using ¹³C NMR, FTIR, and elemental analysis. The phase transition temperatures of the chiral compounds were investigated using X-ray diffraction, differential scanning calorimetry, and polarizing optical microscopy. The thermogravimetric characteristics, the glass-transition temperatures (T_g) and the weight-average molecular weights (M_w) of the homopolymers were also evaluated. Polymers containing chiral menthyl groups with a biphenyl segment were found to reveal high thermal resistance. However, the existence of the steric hindered menthyl group disturbed the arrangement of chiral monomers leading to the disappearance of liquid crystal phases. The specific optical rotation of the synthesized monomers and polymers were also evaluated. The effect of the synthesized chiral compounds, monomers and photoisomerizable azobenzene derivative on the induction of the cholesteric liquid crystal films was investigated. The morphological network structure of the polymer matrix inside a liquid crystal cell was studied using a scanning electron microscope (SEM). The phototuning ability of the AzoM on the cholesteric liquid crystals was also established.     

Asymmetric Epoxidation of Styrene on the Heterogenized Chiral Salen Complexes Prepared from Organo-Functionalized Mesoporous Materials

Organosilane-modified mesoporous materials have been prepared under mild and acidic conditions by a solvent evaporation method using C₁₆TMABr surfactant as a template. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained under hydrothermal conditions had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on these organosilane-functionalized mesoporous silicas by a grafting method. The catalysts used in the asymmetric epoxidation of styrene and cis-stilbene and the effect of different mesoporous structures on the reactivity was investigated. Similar enantioselectivities were observed by using these heterogenized salen complexes as compared with reaction under homogeneous conditions.     

Synthesis and photopolymerizations of new phosphonated methacrylates from alkyl α‐hydroxymethacrylates and glycidyl methacrylate

Novel aromatic mono‐ and di(phosphonate) or phosphonic acid monomers for use in dental composites were synthesized. Synthesis of monomer 1a involved three steps: (i) reaction of t‐butyl α‐bromomethacrylate (t‐BuBMA) and Bisphenol A, (ii) conversion to diacid chloride derivative using thionyl chloride, (iii) reaction of diacid chloride with diethyl (2‐hydroxyphenyl) phosphonate. Monomer 2a was synthesized from the reaction of 2‐chloromethacryloyl chloride and diethyl (2‐hydroxyphenyl) phosphonate. Synthesis of monomer 3a involved reaction of glycidyl methacrylate (GMA) with diethyl (2‐hydroxyphenyl) phosphonate. Hydrolysis of the phosphonate groups of monomers 1a and 2a with trimethylsilyl bromide (TMSBr) gave monomers 1b and 2b with phosphonic acid functionality, which is intended to improve binding ability of dental composites. The homopolymerization and copolymerization behaviors of the synthesized monomers with (Bis‐GMA) were investigated using photodifferential scanning calorimetry at 40°C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as photoinitiator. The interaction of the monomer 1b with hydroxyapatite (HAP) was investigated using Fourier transform infrared technique. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improvement in the synthesis of 2-(5-amino-1,2,4-thiadiazol-3-yl)-2-(Z)-methoxyiminoacetic acid 2-benzothiazolyl thioester

2-(5-Amino-1,2,4-thiadiazol-3-yl)-2-(Z)-methoxyiminoacetic acid 2-benzothiazolyl thioester(III), an important intermediate of the fourth generation cephalosporins, was efficiently synthesized by reacting 2-(5-amino-1,2,4-thiadiazol-3-yl)-2-(Z)-methoxyiminoacetic acid (I) with 2,2′-dibenzothiazole disulfide (II) in the presence of triphenylphosphine. Effects of reaction time, temperature, solvents, catalysts and feeding molar ratio on the yield and quality of products were investigated, and an improved procedure suitable for industrial production was established. Using 1,2-dichloroethane as solvent, triphenylphosphine as reducer, and triethylamine as catalyst, n(I): n(II): n(triphenylphosphine)51.0: 1.0: 1.0, the product was obtained at room temperature in 98.1% yield. The purity of the product without further purification is 98.7% determined by HPLC method. This procedure could be a suitable alternative to the traditional processes because of its easy handling, high yield and low cost. __________ Translated from Fine Chemicals, 2007, 24(8): 816–819 [译自:精细化工]     

Synthesis of p-substituted tetraphenylporphyrins and corresponding ferric complexes with mixed-solvents method

By using mixed-solvents method, five kinds of p-substituted tetraphenylporphyrin compounds [T(p-R)PPH₂, R=NO₂, Cl, CH₃, OCH₃, OH] were synthesized by the condensation of p-substituted benzaldehyde with pyrrole in mixed solvents (propionic acid, acetic acid and nitrobenzene), and corresponding ferric complexes [T(p-R)PPFe^IIICl] were synthesized in dimethylformamide. The above free base porphyrins were obtained in 30%–50% yields, metalation yields were up to 90% and total yields of ferric complexes were 27%–50%. Effects of reactive conditions, solvents and oxidants on yields of free base porphyrins were investigated and the relevant mechanism was discussed. Structures of the above porphyrin complexes were characterized by ultravioletvisible (UV-Vis), infrared (IR) and far infrared (FIR) spectroscopy.     

Fabrication and in vitro degradation study of novel optically active polymers derived from amino acid containing diacids and 4,4′-thiobis(2-tert-butyl-5-methylphenol)

Chiral bioactive poly(ester-imide)s (PEI)s were synthesized from N,N′-(pyromellitoyl)-bis-(L-phenylalanine) and N,N′-(pyromellitoyl)-bis-(L-leucine) diacids derived from amino acids with 4,4′-thiobis(2-tert-butyl-5-methylphenol) via direct polycondensation reaction in a system of tosyl chloride, pyridine and N,N-dimethylformamide as a condensing agent. The structures of these polymers were confirmed by FT-IR, ¹H-NMR, specific rotation, elemental and thermogravimetric analysis (TGA) techniques. TGA showed that the 10% weight loss temperature in a nitrogen atmosphere was more than 390 °C, which indicates that the resulting PEIs have a good thermal stability. The biodegradability of the monomers and prepared polymers was investigated in culture media and soil burial test for assessing the susceptibility of these compounds to microbial degradation. The results showed that the synthesized monomers and theirs derived polymers are biologically active and they are nontoxic to microbial growth.     

The synthesis and evaluation of cyclic olefin sulfone copolymers and terpolymers as electron beam resists

Poly(cyclopentene sulfone) (PCPS) and poly(bicycloheptene sulfone) (PBCHS) copolymers have been evaluated as potential positive electron beam resists which have good thermal properties and which show high sensitivity to ionizing radiation. It was found that thin copolymer films could be processed as resists but that films greater than 3000 Å thick cracked in the solvents used to dissolve the radiation-exposed regions. Incorporation of plasticizing additives did not improve the film properties. Films from low molecular weight polymer fractions cracked less in solvents, but higher radiation doses were required to offset the reduced sensitivity. This resulted in the formation of intractable residues in the exposed regions which appear to be crosslinked polymer. Bicycloheptene monomers with specific functional groups did not improve the properties of the copolymer films. Terpolymerization with α-olefins such as butene-1 and cis-2-butene plasticized these films and reduced their tendency to crack in solvents. Poly(cyclopentene sulfone–co–butene-1 sulfone) films were found to have the best properties, and 1.25-μ resist images could be etched in SiO₂ layers at an exposure dose of 4 × 10^?6 C/cm² at 25KV. However, one important limitation of this terpolymer was the low dissolution rate ratio between the exposed and unexposed regions. Since straight-walled relief images are essential to the formation of high-resolution patterns, the usefulness of this terpolymer as an electron beam resist appears to be hindered by the limited choice of good solvents to maximize the dissolution rate ratio. PBCHS block terpolymers containing methyl methacrylate (MMA) or methacrylic acid (MAA) were synthesized to improve the solubility in solvents and to incorporate the properties of methacrylates. PBCHS–MMA films cracked in solvents after irradiation; PBCHS–MAA polymers were too insoluble to form resist films.     

Synthesis of cis-12, 13-epoxy-cis-9-octadecenol and 12(13)-hydroxy-cis-9-octadecenol from vernonia oil using lithium aluminum hydride

Reduction of vernonia oil methyl esters (VOME) into epoxy fatty alcohol and diols was achieved with lithium aluminum hydride (LAH), under reflux and room temperature conditions, by using hexane and tetrahydrofuran (THF) as solvents. The reactions of VOME with LAH in hexane produced cis-12,13-epoxy-cis-9-octadecenol as a major product with an isolated yield of 73.6%, whereas the reaction with LAH in THF gave isomers of 12(13)-hydroxy-cis-9-octadecenol as the major products with an isolated yield of 95.1%. LAH was similarly reacted with vernonia oil (VO) to give the same products in lower yields. ¹H nuclear magnetic resonance (NMR), ¹³C NMR, gas chromatography-mass spectrometry, and infrared were used to characterize these products. This study demonstrates the ability to control the reactivity of the epoxy functionality in VO or VOME with the choice of polar or nonpolar solvents, and extends the range of oleochemicals that can be derived from vernonia oil.