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Synlett 2008(20): 3141-3144  
DOI: 10.1055/s-0028-1087412
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Catalytic Asymmetric Allylation of Aliphatic Aldehydes by Chiral Bipyridine N,N′-Dioxides

Radim Hrdinaa, Thomas Boyda,1, Irena Valterováb, Jana Hodačováb, Martin Kotora*a,b
a Department of Organic and Nuclear Chemistry, Faculty of Science, Charles University, Hlavova 8, 12843 Praha 2, Czech Republic
Fax: +420(2)21951324; e-Mail: kotora@natur.cuni.cz;
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo n. 2, 16610 Praha 6, Czech Republic
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Publication History

Received 11 August 2008
Publication Date:
26 November 2008 (online)

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Abstract

A new class of axially chiral bipyridine N,N′-oxides with bis(tetrahydroisoquinoline) framework were tested as catalysts in the reaction of aliphatic aldehydes with allyl(trichloro)silane to afford homoallylic alcohols. The course of the reaction, that is, the catalytic activity as well as enantioselectivity, is strongly dependent on the solvent used. The products were obtained in good yields and up to 68% ee in chloroform.

Key Words

allylations - aldehydes - Lewis base - asymmetric catalysis - solvent effect

1

Erasmus-Socrates exchange student from Glasgow University, Glasgow, Scotland.

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General Procedure for Catalytic Allylation of Aliphatic Aldehydes with Allyl(trichloro)silane
To a solution of 1 (0.01 mmol) in a solvent (2 mL) were added aldehyde (1 mmol) and di(isopropyl)ethylamine (155 mg, 208 µL, 1.2 mmol). The temperature was adjusted to either -40 ˚C, -50 ˚C, -55 ˚C, or -78 ˚C before addition of allyl(trichloro)silane (210 mg, 170 µL, 1.2 mmol) and the reaction mixture was stirred for 1-24 h. Then it was quenched with sat. aq NaHCO3 (2 mL), the organic layer separated and dried over MgSO4. Yields and ee of homoallylalcohols 3a-c were determined by GC (HP-Chiral β, 30 m × 0.25 mm, oven: 70 ˚C, then 0.5 ˚C/min to 170 ˚C, flow: 1.5 mL/min), ees of 3d-f were determined by ¹9F NMR of the corresponding esters derived from (S)-Mosher acid chloride. All homoallylalcohols are known compounds and the spectral properties of 3a,¹³ 3b,¹4 3c,¹5 3d,¹6 3e,¹6 and 3f ¹³ were in accordance with the previously reported values. The configuration of the major enantiomer for 3a,¹³,¹7 3b,¹8 3c,¹8 and 3f ¹9 was based on comparison with known optical properties.

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Catalysis by ( R , S , R )-1c
Aldehyde 2a in CHCl3 at -40 ˚C: (R)-(+)-3a, [α]D +5.71 (c 0.005, CH2Cl2), [t R (S) = 68.10 min, t R (R) = 68.69 min), 68% ee (77% yield).
Aldehyde 2b in CHCl3 at -40 ˚C: (S)-(-)-3b, [α]D -3.00 (c 0.005, CHCl3), (t R (R) = 32.62 min, t R (S) = 33.22 min), 56% ee (84% yield).
Aldehyde 2c in CHCl3 at -40 ˚C: (S)-(-)-3c, [α]D -2.50
(c 0.005, CH2Cl2), (t R (S) = 65.92 min, t R (R) = 67.30 min), 64% ee (79% yield).
Aldehyde 2d in CHCl3 at -40 ˚C: (R)-(-)-1-cyclopentyl-but-3-en-1-ol (3d), [α]D -3.33 (c 0.005, CH2Cl2), 68% ee (91%, yield; absolute configuration was estimated by comparison of properties with analogical compounds).
Aldehyde 2e in CHCl3 at -40 ˚C: (R)-(-)-1-cyclopropyl-but-3-en-1-ol (3e), [α]D -2.50˚ (c 0.005, CH2Cl2), 42% ee (90% yield; absolute configuration was estimated by comparison of properties with analogical compounds).
Aldehyde 2f in CHCl3 at -40 ˚C: (S)-(-)-1-tert-butyl-but-3-en-1-ol (3f), [α]D -3.33 (c 0.005, C6H6), 22% ee (10% yield).