Preparation of Chiral Bisoxazolines: Observations on the Effect of Substituents

Denmark, Scott E.; Nakajima, Noriyuki; Nicaise, Olivier J.‐C.; Faucher, Anne‐Marie; Edwards, James P.

doi:10.1021/jo00120a036

Cited by 155 publications

(61 citation statements)

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“…[41] Most commonly, an amino alcohol is condensed with a malonic acid derivative. The resulting bis(hydroxy amide) is cyclized to the bisoxazoline using one of a number of methods, such as treatment with SOCl 2 or activation of the terminal hydroxyl as a mesylate then treatment with base.…”

Section: Preparation Of Chiral Ligandsmentioning

confidence: 99%

Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines

et al. 2008

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The enantioselective addition of organolithium reagents to N-anisyl aldimines promoted by chiral bisoxazolines and (−)-sparteine as external ligands is described. This reaction proceeds readily with a wide range of aldimine substrates (aliphatic, aromatic, olefinic) and organolithium nucleophiles (Me, n-Bu, Ph, vinyl) in excellent yields (81-99%) and with high enantioselectivities (up to 95.5:4.5 er). The external ligands can be used in substoichiometric amounts albeit with slightly attenuated enantioselectivities. A systematic evaluation of the structural features of the bisoxazolines revealed a primary contribution from the substituent at C(4) and a secondary influence from the bridging substituents. A computational analysis (PM3) provided a clear rationalization for the origin of enantioselectivity.

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Section: Preparation Of Chiral Ligandsmentioning

confidence: 99%

Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines

et al. 2008

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“…21 -150.7°, c = 1.0 g dL -1 , THF, l = 10 em). Commercially available (-)-sparteine (Sp) was purified by distillation under reduced pressure: bp 93-94oC I 5X10-2 mmHg; -10.3° (c = 1.0 g dL -1, THF, l = 10 em).…”

Section: Methodsmentioning

confidence: 98%

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

Zhou

Onimura

Tsutsumi

et al. 2001

Polym J

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ABSTRACT:Chiral (S )-(-)-N-a-methylbenzylmaleimide ((S )-(-)-MBZMI) was polymerized with chiral complexes of (-)-sparteine (Sp) or (S, S )-(1-ethylpropylidene)bis(4-benzyl-2-oxazoline) (Bnbox) with organometal in toluene or tetrahydrofuran (THF). Specific rotations ofthe polymers obtained by Et2Zn1Sp and Et2Zn1Bnbox were +20.5° to +466.2° and + 9.4° to +39.5°, respectively. In the asymmetric anionic polymerization of (S )-(-)-MBZMI, Sp was found a more effective chiral ligand than Bnbox. Chirality of the polymers was mainly attributed to different ratios between stereogenic centers (S, S) and (R, R) in the main chain produced by asymmetric induction. Crystalline poly((S )-(-)-MBZMI)s obtained with Et2Zn1Sp at lower temperatures in toluene having specific rotations more than +200° showed higher stereoregularity, compared to that of poly((R )-( + )-MBZMI) under the same conditions, judging from XRay diffraction diagrams and 13 C NMR spectra. Chiroptical properties of these polymers may partially be due to helical conformation.KEY WORDS Chiral N-Substituted Maleimide I Chiral Ligand I Asymmetric Anionic Polymerization I Optically Active Polymer I Crystallinity I Asymmetric anionic polymerizations of bulky methacrylate, isocyanate and acetylene derivatives with chiral ligand-organometal complexes were systematically carried out by Okamoto et al. to give optically active polymers with one handed-helical conformation. 1 -3Up to now, asymmetric anionic polymerizations of achiral N-substituted maleimide (RMI) 4 -11 have been studied using chiral ligand-organometal complexes to obtain optically active poly(RMI). More recently, the authors obtained optically active poly(RMI) with higher specific rotations. 5 -1° Chirality of the polymers was attributed to excess chiral stereogenic centers (S, S) and (R, R ) in the polymer main chain based on threodiisotactic structures formed from asymmetric polymerization. Polymerizations and copolymerizations of chiral RMI have been studied by the authors. 12 -16 A new chirality was introduced onto the main chain of poly-(RMI) in spite ofpoly(RMI) having small specific rotation.

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“…40 Radical initiator, 2,2 0 -azobisisobutyronitrile (AIBN) (Ishizu Seiyaku, Ltd.) was purified by recrystallization from methanol. Palladium-activated carbon (Wako Pure Chemical Industries, Ltd., Pd 10%) was used as purchased.…”

Section: Reagentsmentioning

confidence: 99%

Asymmetric Polymerizations of N-Substituted Maleimides Bearing L-Leucine Ester Derivatives and Chiral Recognition Abilities of Their Polymers

Oishi

Gao

Nakamura

et al. 2007

Polym J

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ABSTRACT:Two kinds of N-substituted maleimides bearing L-leucine ester derivatives ((S)-RLMI), i.e. (S)-Nmaleoyl-L-leucine methyl ester ((S)-MLMI) and (S)-N-maleoyl-L-leucine benzyl ester ((S)-BnLMI), were synthesized from maleic anhydride, L-leucine, and corresponding alcohols. Asymmetric polymerizations were carried out to obtain optically active polymers. Specific rotations of the poly (RLMI)s were influenced by N-substituents, initiators, solvents and temperature. Chiroptical properties and structures of the poly((S)-RLMI)s obtained were investigated by GPC, CD, and NMR measurements. Optical activities of the poly((S)-RLMI)s obtained with anionic polymerization were attributed to excessive chiral centers of the main chain induced through the polymerizations in addition to the chirality of the N-substituents. The chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC) were prepared and the chiral recognition abilities of the optically active poly((S)-RLMI)s were also discussed.

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Preparation of Chiral Bisoxazolines: Observations on the Effect of Substituents

Cited by 155 publications

References 0 publications

Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines

Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines

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

Asymmetric Polymerizations of N-Substituted Maleimides Bearing L-Leucine Ester Derivatives and Chiral Recognition Abilities of Their Polymers

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