Synthesis and Chiroptical Properties of (S)-(−)-N-α-Methylbenzylmaleimide Polymers Containing Crystallinity

Oishi

et al. 2011

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Novel optically active (S)-2-(3,5-diiodophenyl)oxazoline derivatives ((S)-DIPhROx)) (R¼4-benzyl (1a), 4-phenyl (1b)) were synthesized and polymerized using the Sonogashira-Hagihara coupling reaction to obtain the poly(phenylene-ethynylene)s bearing oxazoline derivatives in the weight range from 1060 to 17 300 in 40-72% yields. The polymers were thermally stable up to 220 1C. All the polymers exhibited higher specific rotation values than the model compound did. Moreover, these polymers also showed intense circular dichroism (CD) signals in the transition region of the conjugated main chain, whereas almost no induced Cotton effect was observed for the model compound. The results of the specific rotation and CD and ultraviolet analyses indicate that the optical activities of the polymers arise not only from the configurational chirality of the optically active oxazoline pendant groups but also from elements of higher-order structure such as the helical conformation.

Section: Monomer Synthesismentioning

confidence: 99%

Synthesis and characterization of optically active poly(phenylene-ethynylene)s containing chiral oxazoline derivatives

Rattanatraicharoen

Oishi

et al. 2011

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“…6,[8][9][10][11][12][13][14][15][16][17] Among the optically active poly(RMI)s, the RMI with an achiral 1-naphthyl or a chiral (S)-methylbenzyl group as an N-substituent showed the highest specific optical rotation in chloroform ([a] 435 ¼+762.31, +551.71). [10][11][12] Recently, we reported on the asymmetric polymerizations of achiral maleimide bearing an achiral benzo crown ether and additional effects of the chiral amine on the achiral polymers. 17 However, there have been no reports on the asymmetric polymerization of chiral maleimide bearing an amino-acid moiety and aza crown ether derivatives.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and asymmetric polymerization of chiral maleimides bearing an aza crown ether

Azechi

Iwai

et al. 2011

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Chiral N-substituted maleimide derivatives bearing L-phenylalanine-or L-leucine-introduced aza crown ether ((S)-A15C5PAMI, (S)-A15C5LMI) were synthesized from maleic anhydride, corresponding amino acids and aza crown ether, and polymerized with an organometal/chiral ligand. The number-average-molecular weights and the specific optical rotations of the polymers were 700-5600 and À105.81 to À38.31, respectively. The specific optical rotations of all polymers tended to a positive direction, Keywords: amino acid; anionic polymerization; asymmetric polymerization; aza crown ether; maleimide INTRODUCTIONThe synthesis of optically active polymers is interesting from the standpoints of the formation process, stereoregularity and asymmetric functionality. The optical activity of these polymers is dependent on the main chain forming a one-handed helical structure. The main chain structure of these optically active polymers is very important for special functions such as molecular recognition and asymmetric catalysis. To artificially form a one-handed helical structure, it is necessary to synthesize an optically active polymer by asymmetric polymerization. For example, Okamoto and coworkers [1][2][3][4] reported that the polymers obtained from the asymmetric polymerization of methacrylate derivatives bearing bulky substituents showed substantial optical activity on the basis of one-handed helical conformations.N-Substituted maleimides (RMIs) have been well known as a type of attractive monomer that provides optically active polymers through asymmetric anionic polymerization. 5,6 Because the RMI has a 1,2-disubstituted structure, poly(RMI) can be presumed to produce four types of structures: threo-diisotactic, threo-disyndiotactic, erythrodiisotactic and erythro-disyndiotactic. Erythro-diisotactic and erythro-disyndiotactic structures cannot be formed with cis-additional reactions because of steric hindrance among monomeric units due to carbonyl groups in the imide rings. 7 Trans-additional structures, that is, threo-diisotactic and threo-disyndiotactic structures, can be formed during the polymerization of RMI. Threo-disyndiotactic structures show no optical activity because the (S, S)-and (R, R)-configurational pairs exist at equivalent levels in the polymer main chains. Poly(RMI) with a threo-diisotactic structure can show optical activity when one of the asymmetric carbon pairs in the monomer unit exists in excess. Furthermore, the high continuity of the same configurational pair

“…In recent years, our research focus has been on the asymmetric polymerization of RMIs bearing amino-acid derivative moieties, and we have reported the higher-order structure of polymers induced by hydrogen bonding between the amino-acid side chains. [16][17][18][19][20][21][22][23] An N-substituted itaconimide (RII) is a five-membered ring compound and RMI, but RII is different from RMI in the position of the double bond; that is, RII is a 1,1-disubstituted ethylene. 24,25 Therefore, it is hoped that the polymers obtained from asymmetric polymerization of RII have conformational chirality based on the structure of the main chain and bulky methacrylate reported previously.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Asymmetric anionic polymerizations of N-substituted itaconimides having chiral amino-acid esters

Hashino

Azechi

et al. 2011

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Chiral itaconimides bearing the amino-acid methyl ester (MRII), such as phenylglycine-, phenylalanine-and leucine-methyl ester, at the side chain (S)-or (R)-MPGII, (S)-MPAII and (S)-MLII, respectively, were successfully synthesized and then polymerized with organometal-chiral ligand complexes such as n-butyllithium/(À)-sparteine [n-BuLi/(À)-Sp], n-BuLi/(S,S)-(1-ethylpropylidene)bis(4-benzyl-2-oxazoline) [n-BuLi/(S,S)-Bnbox], Et 2 Zn-(À)-Sp and Et 2 Zn-(S,S)-Bnbox in toluene or tetrahydrofuran (THF) to obtain optically active polymers. The effects of polymerization conditions on optical activity and the structure of poly(MRII)s were investigated by gel permeation chromatography (GPC), circular dichroism, specific rotation and 13 C nuclear magnetic resonance measurements. The yields of methanol-insoluble part of the polymer and the M n s, as well as the chiroptical properties of poly(MRII)s, were strongly affected by organometals, ligands, solvents and temperature. The behaviors of poly(MRII)s were different according to N-substituents. In addition, the polymers obtained with n-BuLi as the anionic initiator had higher stereoregularity than those obtained with a radical initiator. Polymer Journal (2011) 43, 516-524; doi:10.1038/pj.2011.17; published online 6 April 2011Keywords: amino-acid ester; anionic polymerization; asymmetric polymerization; itaconimide INTRODUCTION Chiral synthetic polymers are particularly interesting because of their applications as chiral stationary phases for high-performance liquid chromatography, chiral catalysts and chiral reagents. Moreover, for the function of biopolymers such as deoxyribonucleic acid (DNA) and protein, it is important to control secondary structures such as helices. Syntheses of helical polymers, such as poly(alkyl methacrylate)s, 1-3 polyacetylenes, 4-7 polyisocianates 8 and polyisocyanides, 9-11 have been reported by several researchers. Physical and steric interactions between side chains are essential factors in the formation of the helical structures of these polymers. For example, Okamoto et al. [1][2][3] reported that polymerization of triphenylmethyl methacrylate with organolithium/chiral ligand complexes successfully proceeded to yield a polymer with a single-handed helical structure formed by steric repulsion between the bulky side chains. Masuda et al. 12-15 successfully synthesized poly(N-propargylamide)s with a well-controlled helical structure based on hydrogen bonding between the chiral side chains, as well as steric repulsion.We systematically investigated the asymmetric polymerization of N-substituted maleimides (RMIs) and reported properties of the resulting polymer with chiral recognition ability. In recent years, our research focus has been on the asymmetric polymerization of RMIs bearing amino-acid derivative moieties, and we have reported the higher-order structure of polymers induced by hydrogen bonding between the amino-acid side chains. [16][17][18][19][20][21][22][23]