• Bulletin of the Korean Chemical Society
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• 제26권6호
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• pp.989-992
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• 2005

Dynamic kinetic resolution of $\alpha$-bromo carboxylic acid derivatives in nucleophilic substitution with chiral $\alpha$-amino ester nucleophiles in the presence of TBAI and DIEA has been investigated for stereoselective syntheses of 1,1'-iminodicarboxylic acid derivatives. Nucleophilic substitutions with various chiral $\alpha$-amino esters gave iminodiacetates 2-8 with stereoselectivities up to 87 : 13 dr. Also, the reactions of N-($\alpha$-bromo-$\alpha$-phenylacetyl)-L-alanine methyl ester with L-alanine, D-alanine and glycine methyl ester nucleophiles afforded N-carboxyalkyl dipeptide analogues 10-12 up to 90 : 10 dr.

• Bulletin of the Korean Chemical Society
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• 제15권9호
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• pp.732-739
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• 1994

Asymmetric [2,3]-Wittig rearrangements of allyl propargyl ethers in hexane were performed in the presence of s-butyllithium and (-)-${\alpha}$-isosparteine which is a $C_2$-symmetric chiral ligand for the alkyllithium reagent. The reactions of (Z)-or (E)-allyl 3-trimethylsilylpropargyl ethers at -78$^{\circ}C$ showed good diastereoselectivities (74-100%) and moderate enantioselectivities (29-71%). The absolute configurations of the rearrangement products were determined by the corresponding Mosher's esters. It was found that (-)-${\alpha}$ -isosparteine induced (R) configuration at the hydroxy carbon and syn stereochemistry more favorably. The possible transition state is discussed.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.565-569
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• 1991

Enantioselective synthesis of 1-substituted tetrahydroisoquinoline alkaloids (1) via asymmetric reduction of 1-substituted 3,4-dihydroisoquinolines (2) and the corresponding iminium salts (3) with the selected chiral hydride reagents, such as K glucoride (5), Itsuno's reagent (6), and Mosher's reagent (7) were examined. In these reactions, dihydroisoquinolines were not reduced by the hydride reagents, whereas the iminium salts were easily reduced under the same reaction conditions found in successful reduction of ketones. Thus, the reduction of 6,7-dimethoxy-3,4-dihydroisoquinolium iodide(3a) with 5, 6 and 7 provided the product 1a with 52.3 % ee, 18 % ee, and 66.4 % ee, respectively. For 1-benzyl derivatives (3b-3d), syntheses of 1b-1d with 0.7-6.2 % ee, 5.9-21 % ee, and 1.4-2.7 % ee were achieved with chiral reducing agents 5, 6 and 7, respectively. For 1-aryl derivatives, use of 5, 6 and 7 resulted in optical inductions in the range of 25.2-43 % ee, 13-21.1 % ee, and 6.3-16 % ee, respectively.

• Bulletin of the Korean Chemical Society
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• 제12권6호
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• pp.662-665
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• 1991

In order to prepare new chiral borohydrides (4) possessing chirality on dialkyl moieties, a series of B-alkoxydiisopinocampheylborinates (3) were synthesized by treatment of diisopinocampheylborane ($Ipc_2BH$) with alcohols (R in ROH: Me, Et, i-Pr, t-Bu) and reacted with excess of potassium hydride. Of these chiral borinic esters, only B-methoxydiisopinocampheyl borinate (3a) was converted into the corresponding dialkylmonoalkoxyborohydride (4a). For the other borinic esters, hydride uptake reactions were very slow at room temperature, accompanying disproportionation products at $65^{\circ}C$. The hydride (4a) formed is stable at $0^{\circ}C$ and can be stored over potassium hydride for few months. In the asymmetric reduction of the selected ketones, 4a provided the corresponding alcohols, such as 21% ee for 3-methyl-2-butanone, 11% ee for 2,2-dimethylcyclopentanone, 24% ee for acetophenone, 32% ee for 3-acetylpyridine, 30% for methyl benzoylformate, 31% ee for 4-phenyl-3-butyn-2-one, 39% ee for 3-butyn-2-one, and 34% ee for 3-hexyn-2-one.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2435-2441
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• 2007

The catalytic enantioselective electrophilic fluorinations of active methane compounds promoted chiral palladium complexes have been developed. Treatment of α-cyano acetates and α-cyanoalkylphosphonates with N-fluorobenzenesulfonimide as the fluorine source under mild reaction conditions afforded the corresponding α-cyano-α-fluorinated adducts in high yields with excellent enantiomeric excesses (up to 99% ee). These reactions can be conducted in alcoholic solvents without any precaution to exclude water and moisture.

• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2045-2050
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• 2007

The reactions of mercury(II) chloride with O3S2-donor macrocyclic ligands with (L1) and without (L2) dibenzosubunit afforded respective exo- (1) and endo-coordinated (2) complexes depending on the ring rigidity of the ligands. From the X-ray crystal structures and comparative NMR studies for the complexes 1 and 2, it is confirmed that the resulting species with different coordination modes exist not only in solid state but also in solution state.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2527-2530
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• 2010

The stereoselectivity of the intramolecular Diels-Alder reactions of 1 and its derivatives were investigated by ab initio calculations. The stereoselectivity mainly originates from the steric repulsion and the orbital interactions. The additional s-cis and s-trans conformations by introducing the carbonyl group at the neighbor of diene or dienophile may change the stereoselectivity, hence this kind of substitution can be utilized for stereoselectivive asymmetric synthesis.

• Bulletin of the Korean Chemical Society
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• 제29권2호
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• pp.313-318
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• 2008

An enantioselective ring opening of racemic terminal epoxides has been achieved by using heterobimetallic cobalt salen complexes with variety of nucleophiles. They were proven to be highly enantioselective and reactive for the synthesis of valuable chiral building blocks in enantio-riched forms up to 98% ee.

• Bulletin of the Korean Chemical Society
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• 제19권4호
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• pp.475-481
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• 1998

Details of various equilibria involved in the reactions of oxaza- and thiazazincolidine catalysts, generated from either β-amino alcohol or β-amino thiol, with aldehyde were studied by colligative measurements. The results indicated that the coordination of diethylzinc prior to the coordination of aldehyde is essential for high enantioselectivity of the thiol catalyzed reaction. The probable origin of asymmetric nonlinearity is also presented.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.198-198
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• 2011

Organocatalysis is a relatively new and popular area within the field of chiral molecule synthesis. It is one of the main branches of enantioselective synthesis with enzymatic and organometallic catalysis. In recent years, immense high quality studies on catalysis by chiral secondary amines were reported. These progresses instantly led to different organocatalytic activation concepts, so thousands of researchers from academia and the chemical industry are currently involved in this field and new ideas, new approaches, and creative thinking have been rapidly emerged. Organocatalysts, some of which are natural products, appear to solve the problems of metal catalysts. Compared to metal-based catalysis, they have many advantages including savings in cost, time, and energy, easier experimental procedure, and reduction of chemical waste. These benefits originate from the following factors. First, organocatalysts are generally stable in oxygen and water in the atmosphere, there is no need for special equipments or experimental techniques to operate under anhydrous or anaerobic conditions. Second, organic reagents are naturally available from biological materials as single enantiomers that they are easy and cheap to prepare which makes them suitable for small-scale to industrial-scale reactions. Third, in terms of safety related catalysis, small organic molecules are non-toxic and environmentally friendly. Therefore, the purpose of this research is to develop novel synthetic methods and design for various organocatalyst. Furthermore, it is expected that these organocatalysts can be applied to a variety of asymmetric reactions and study the transition state of these reactions using a metal sulface. Here, we report the synthesis of unprecedented organocatalysts, proline and pyrrolidine derivatives with quaternary carbon center.