Enantioface differentiation by chiral polymers having (+)‐5,6‐<i>exo</i>‐bornanediol moieties. II. Asymmetric reduction of prochiral ketones by chiral polymers containing (+)‐5,6‐<i>exo</i>‐bornanediol derivatives

Liu, Jui-Hsiang; Lin, Shyuh‐Rurng; Kuo, Jue‐Cheng ‐C

doi:10.1002/pola.1987.080250917

Cited by 9 publications

References 14 publications

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Enantioselective Reduction of Ketones

Itsuno

1998

Organic Reactions

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Enantioselective reduction of prochiral ketones is among the most important methods for preparing enantioenriched secondary alcohols, which are important starting materials for a number of enantiopure compounds, including natural products. Various methods for enantioselective reduction of ketones have been developed for producing enantioenriched alcohols. These methods involve the use of both stoichiometric reagents and catalytic reductions. Metal hydride reagents such as lithium aluminum hydride (LAH) and sodium borohydride (NaBH 4 ) are easily modified by enantiopure compounds. For example, binaphthol‐modified aluminum hydride reagent (BINAL‐H) is a derivative of LAH in which the enantiopure diol 1,1′‐bi‐2‐naphthol and one other alcohol replace three of the hydrogens. This reagent achieves high selectivity in many ketone reductions. The other impressive area of success is the use of enantiopure alkylboranes. The β hydride of enantiopure alkylboranes is delivered selectively, often exclusively, to one face of the carbonyl group of a ketone. Despite remarkable success with stoichiometric reagents, their important drawback is that at least one equivalent of reagent is required for reduction of the ketone. Thus catalytic processes are desirable for enantioselective ketone reduction as well as for other asymmetric transformations. Hydrogenation and hydrosilylation of ketones are catalyzed by transition metal catalysts. Enantiopure ligand‐transition metal complexes can be used as asymmetric catalysts for these reactions. Recent research makes it possible to achieve high enantioselectivity, not only for the reduction of functionalized ketones in which a transition metal can coordinate to an adjacent functional group, but also for simple ketones such as acetophenone. One of the most remarkable catalytic systems described in recent years is borane reduction in the presence of an oxazaborolidine, which contains adjacent donor (nitrogen) and acceptor (boron) sites. Many biologically active compounds have been synthesized by using oxazaborolidine‐catalyzed borane reductions of ketones as the key step. Asymmetric reduction with enzymes is another important method. Some baker's yeast mediated ketone reductions have practical applicability. This chapter addresses the enantioselective reduction of ketones by various methods including chirally modified hydride reductions, oxazaborolidine catalyzed reductions, Meerwein‐Ponndorf‐Verley (MPV) reductions, hydrogenations, hydrosilylations, and enzymatic reductions.

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Enantioselective Reduction of Ketones

Itsuno

1998

Organic Reactions

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Synthesis of chiral polymers containing dimethylaminobornanol moieties

Liu

1988

Angew. Makromol. Chem.

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In order to investigate the influence of spacer on the stereoselectivity of the addition of n‐butyllithium to aldehydes, three kinds of chiral polymers containing dimethylaminobornanol moieties were synthesized. The polymerization of the chiral monomers was carried out under various conditions. Cross‐linked chiral polymers were prepared by copolymerization of the chiral monomers with commercial p‐divinyl benzene. The conversion was found to be affected by the kind of solvents. Asymmetric addition of n‐butyllithium to benzaldehyde was carried out in the presence of the chiral polymers having dimethylaminobornanol moieties, and it was found that all three kinds of chiral polymers are effective for the asymmetric addition. Advantages of insoluble chiral polymers such as the ease of separation from products and the ability to be recycled, are discussed.

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Asymmetric addition of n‐butyllithium to aldehydes by chiral polymers having acetoxybornyl moieties

Liu

Kuo

1992

Angew. Makromol. Chem.

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Optically active (+)-2-endo-acetoxy-5-endo-bornyl methacrylate (ABMA) was prepared from (+)-camphor. The free-radical homopolymerization of ABMA and its copolymerization with achiral methyl methacrylate (MMA) or styrene (St) were carried out with 2,2'-azoisobutyronitrile in benzene. Effects of temperature and reaction time on the copolymerization were discussed. The monomer reactivity ratios (r,, r2) for poly(ABMA-co-MMA) and poly(ABMA-co-St) as well as Q and e values for the chiral ABMA in the copolymerization systems were evaluated by the Fineman-Ross method. It was found that 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 nbutyllithium to aldehydes were investigated. The effect of temperature and aldehydes on the asymmetric addition were also discussed. ZUSAMMENFASSUNG:Optisch aktives ( + )-2-endo-Acetoxy-5-endo-bornylmethacrylat (ABMA) wurde aus (+)-Campher hergestellt und in Benzol radikalisch homo-bzw. mit achiralem Methylmethacrylat (MMA) bzw. Styrol (St) copolymerisiert. Der EinfluB von Temperatur und Reaktionszeit auf den Polymerisationsverlauf wird diskutiert. Die Copolymerisationsparameter (r, und r2, nach Fineman-Ross) fur Poly(ABMA-co-MMA) und Poly(ABMA-co-St) sowie die Q-und e-Werte fur ABMA wurden berechnet.Der Absolutwert der spezifischen Drehung von Poly(ABMA-co-MMA) nimmt mit steigendem ABMA-Gehalt im Copolymeren zu. Eine geringe Abweichung von der Linearitat deutet darauf hin, daB die Copolymerhauptkette nicht asymmetrisch ist. Aus der Temperatur-und Lijsungsmittelabhangigkeit der spezifischen Drehung der be-schriebenen Homo-und Copolymeren laBt sich schlierjen, da13 diese nicht in einer speziellen helikalen Konformation vorliegen. Die Eignung der chiralen Polymeren a k Katalysatoren fur die asymmetrische Addition von Butyllithium an verschiedene Aldehyde in Abhangigkeit von der Temperatur wurde untersucht.

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Enantioface differentiation by chiral polymers having (+)‐5,6‐exo‐bornanediol moieties. II. Asymmetric reduction of prochiral ketones by chiral polymers containing (+)‐5,6‐exo‐bornanediol derivatives

Cited by 9 publications

References 14 publications

Enantioselective Reduction of Ketones

Enantioselective Reduction of Ketones

Synthesis of chiral polymers containing dimethylaminobornanol moieties

Asymmetric addition of n‐butyllithium to aldehydes by chiral polymers having acetoxybornyl moieties

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