Stereoselective Addition of Diethylzinc to Aldehydes Using Chiral
               β-Hydroxy-2-oxazolines as Catalysts

Chiral β-hydroxy-2-oxazolines were synthesized and evaluated as catalysts for the addition of diethylzinc to aldehydes. All oxazolines proved effective in obtaining the addition products. The best enantiomeric excesses (69-78%) were obtained using the chiral β-hydroxy oxazoline derived from (−)-menthone and the amino alcohol 2-amino-2-methylpropan-1-ol.

(−)-menthone; chiral β-hydroxy-2-oxazolines; catalysts; diethylzinc; aldehydes

Authorship

Francisco A. Marques ^**e-mail: tic@ufpr.br

Departamento de Química, Universidade Federal do Paraná, P.O. Box 19081, 81531-990 Curitiba-PR, BrazilUniversidade Federal do ParanáBrazilCuritiba, PR, BrazilDepartamento de Química, Universidade Federal do Paraná, P.O. Box 19081, 81531-990 Curitiba-PR, Brazil

Celso L. Wosch

Gustavo Frensch

Ricardo Labes

Beatriz H. L. N. S. Maia

Kahlil S. Salomé

Andersson Barison

Palimécio G. Guerrero Jr

Departamento de Química e Biologia, Universidade Tecnológica Federal do Paraná, P.O. Box 81280-340 Curitiba-PR, BrazilUniversidade Tecnológica Federal do ParanáBrazilCuritiba, PR, BrazilDepartamento de Química e Biologia, Universidade Tecnológica Federal do Paraná, P.O. Box 81280-340 Curitiba-PR, Brazil

*e-mail: tic@ufpr.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (5)
Tables (1)

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Figure 1
Preparation of the chiral β-hydroxy-2-oxazolines.

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Figure 2
Chromatogram obtained with a fused silica column coated with Chirasil-Dex CB-β-cyclodextrin (30 m × 0.25 mm × 0.25 μm) showing the area of elution of ligand 1 in (a) 75:25 diastereomeric ratio and (b) after diastereomeric purification, at 95:5 diastereomeric ratio.

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Figure 3
Determination of the stereochemistry of the major diastereomer of ligand 1 by NOE.

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Table 1
Screening of the conditions to perform the addition of diethylzinc to p-chlorobenzaldehyde using 1 as catalyst

^aYield of isolated product; ^bdetermined by chiral GC (column: β-cyclodextrin-CB); ^cabsolute configuration determined by comparison of the optical rotation with published data;⁷⁰70 Kang, J.; Lee, J. W.; Kim, J. I.; J. Chem. Soc., Chem. Commun. 1994, 2009. ^dligand used in a 95:5 diastereomeric mixture.

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Table 3
Addition of diethylzinc to benzaldehydes using ligand 1 as catalyst

^aYield of isolated product; ^bdetermined by chiral GC (column: CB-cyclodextrin-β); ^cabsolute configuration determined by comparison of the optical rotation with published data.⁷⁰70 Kang, J.; Lee, J. W.; Kim, J. I.; J. Chem. Soc., Chem. Commun. 1994, 2009.

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Table 2
Addition of diethylzinc to p-chlorobenzaldehyde using chiral β-hydroxy-2-oxazolines as catalysts^a a The reaction was carried out using hexane as solvent, 5% molar ratio of ligand, 0 °C, for 2 h;

Figure 1 Preparation of the chiral β-hydroxy-2-oxazolines.

Figure 2 Chromatogram obtained with a fused silica column coated with Chirasil-Dex CB-β-cyclodextrin (30 m × 0.25 mm × 0.25 μm) showing the area of elution of ligand 1 in (a) 75:25 diastereomeric ratio and (b) after diastereomeric purification, at 95:5 diastereomeric ratio.

Figure 3 Determination of the stereochemistry of the major diastereomer of ligand 1 by NOE.

Table 1 Screening of the conditions to perform the addition of diethylzinc to p-chlorobenzaldehyde using 1 as catalyst
^aYield of isolated product; ^bdetermined by chiral GC (column: β-cyclodextrin-CB); ^cabsolute configuration determined by comparison of the optical rotation with published data;⁷⁰70 Kang, J.; Lee, J. W.; Kim, J. I.; J. Chem. Soc., Chem. Commun. 1994, 2009. ^dligand used in a 95:5 diastereomeric mixture.

Table 3 Addition of diethylzinc to benzaldehydes using ligand 1 as catalyst
^aYield of isolated product; ^bdetermined by chiral GC (column: CB-cyclodextrin-β); ^cabsolute configuration determined by comparison of the optical rotation with published data.⁷⁰70 Kang, J.; Lee, J. W.; Kim, J. I.; J. Chem. Soc., Chem. Commun. 1994, 2009.

Table 2 Addition of diethylzinc to p-chlorobenzaldehyde using chiral β-hydroxy-2-oxazolines as catalysts^a a The reaction was carried out using hexane as solvent, 5% molar ratio of ligand, 0 °C, for 2 h;

entry	Ligand	Yield / %^b b yield of isolated product;	e.e. / %^c c determined by chiral GC (column: CB-cyclodextrin-β);
1	1	93	69 (R)^d d absolute configuration determined by comparison of the optical rotation with published data.70
2	2	67	50 (R)
3	3	62	25 (R)

^a
The reaction was carried out using hexane as solvent, 5% molar ratio of ligand, 0 °C, for 2 h;
^b
yield of isolated product;
^c
determined by chiral GC (column: CB-cyclodextrin-β);
^d
absolute configuration determined by comparison of the optical rotation with published data.⁷⁰70 Kang, J.; Lee, J. W.; Kim, J. I.; J. Chem. Soc., Chem. Commun. 1994, 2009.

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Stereoselective Addition of Diethylzinc to Aldehydes Using Chiral β-Hydroxy-2-oxazolines as Catalysts

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[1] *e-mail: tic@ufpr.br