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Synlett 2008(14): 2150-2154  
DOI: 10.1055/s-2008-1077900
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Titanium(IV)(salen) and Vanadium(V)(salen) Complexes Derived from C 2- and C 1-Symmetric Diamines for Asymmetric Cyanohydrin Synthesis

Yuri N. Belokon’b, Jamie Hunta, Michael North*a
a School of Chemistry and University Research Centre in Catalysis and Intensified Processing, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
Fax: +44(870)1313783; e-Mail: Michael.north@ncl.ac.uk;
b A.N. Nesmeyanov Institute of Organo-Element Compounds, Russian Academy of Sciences, Vavilov 28, 119991 Moscow, Russian ­Federation
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Publication History

Received 9 April 2008
Publication Date:
15 July 2008 (online)

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Abstract

Titanium and vanadium salen complexes have been prepared from C2- and C 1-symmetric acyclic diamines. All of the complexes catalysed the asymmetric addition of trimethylsilyl cyanide to benzaldehyde and the sense of asymmetric induction was determined by the nature of the substituents. The vanadium complex of a valine-derived diamine gave good results with a range of aromatic and aliphatic aldehydes.

Key words

cyanohydrins - homogenous catalysis - asymmetric catalysis - Schiff bases - titanium

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11

Benzaldehyde (0.10 mL, 0.98 mmol) and catalyst 5, 6, 8, or 9 (0.1-10 mol%) were dissolved in freshly distilled CH2Cl2 (5 mL). Trimethylsilyl cyanide (0.14 mL, 1.08 mmol, 1.1 equiv) was added, and the reaction was stirred at r.t. overnight. The resulting solution was filtered through a pad of SiO2 using CH2Cl2 as eluent. Solvent was removed in vacuo to give mandelonitrile trimethylsilyl ether as a yellow oil. The conversion was determined by ¹H NMR spectroscopy. The mandelonitrile trimethylsilyl ether and Sc(OTf)3 (1 mol%) were then dissolved in MeCN (5 mL), and Ac2O (2.0 equiv) was added. The reaction mixture was stirred at r.t. for 20 min, then filtered through a pad of SiO2 using CH2Cl2 as eluent. Solvent was removed in vacuo to give mandelonitrile acetate as a yellow oil which was analysed by chiral GC to determine its ee.