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Synlett 2004(9): 1521-1524  
DOI: 10.1055/s-2004-829075
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of a New Chiral Cyclic o-Hydroxynaphthylphosphonodiamide and its Application as Ligand Catalyst in Asymmetric Silylcyanation of Aromatic Aldehydes

Ke He, Zhenghong Zhou*, Lixin Wang, Kangying Li, Guofeng Zhao, Qilin Zhou, Chuchi Tang
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. China
Fax: +86(22)23503438; e-Mail: z.h.zhou@nankai.edu.cn;
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Publication History

Received 24 March 2004
Publication Date:
29 June 2004 (online)

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Abstract

A new chiral cyclic o-hydroxynaphthylphosphonodi­amide (+)-2 was synthesized starting from (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine. The absolute configuration of phos-phorus atom was determined as S by X-ray diffraction analysis. ­Excellent enantioselectivity (up to 98.3% ee) was achieved in asymmetric silylcyanation of aromatic aldehydes using a chiral titanium complex prepared in situ from Ti(Oi-Pr)4 and (+)-2 as the catalyst.

Key words

chiral phosphonodiamide - asymmetric silylcyanation - catalysis - enantioselectivity - aromatic aldehyde

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General procedure for the asymmetric silylcyanation of aromatic aldehydes:

To a solution of (+)-(S)-2 (0.275 g, 0.54 mmol) in 5 mL of methylene chloride was added Ti(OPr-i)4 (37.2 mL, 0.13 mmol) under a nitrogen atmosphere at 20 °C and resulting mixture was stirred for 1 h at the same temperature. Then iso-propanol (15.6 mL, 0.26 mmol), 2 mL of methylene chloride, benzaldehyde (0.142 g, 1.34 mmol) and trimethylsilyl cyanide (200 mL, 16 mmol) were added to it and the whole stirred for 24 h at the same temperature. After determination of the enantiomeric excess value of the cyanohydrin trimethylsilylether by chiral HPLC, the mixture was poured into a mixture of 1 N HCl (30 mL) and ethyl acetate (40 mL) and stirred vigorously for 6 h. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (2 ¥ 20 mL). The combined organic phase was washed with brine and dried over anhydrous magnesium sulfate. After removal of solvent the residue was purified by thin layer chromatography on silica gel to afford 150 mg (84% yield) of the corresponding cyanohydrin. [a]D 20 +23.8 (c 1, CHCl3), 1H NMR (d, CHCl3): 3.51 (s, 1H, OH), 5.48 (d, 1H, CH), 7.43-7.49 (m, 5H, 5 Harom).

Spectroscopic data for all prepared compounds are available from the authors.