Synlett 2011(7): 903-906  
DOI: 10.1055/s-0030-1259698
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Asymmetric Mukaiyama Aldol Reaction Catalyzed by C 2-Symmetric N,N′-Dioxide-Ni(II) Complex

Jiannan Zhao, Ke Zheng, Yang Yang, Jian Shi, Lili Lin, Xiaohua Liu, Xiaoming Feng*
Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, P. R. of China
e-Mail: xmfeng@scu.edu.cn;
Further Information

Publication History

Received 22 September 2010
Publication Date:
08 March 2011 (online)

Abstract

The N,N′-dioxide-Ni(II) complex has been developed for the asymmetric Mukaiyama aldol reaction between glyoxal derivatives and enolsilane which produced the 2-hydroxy-1,4-dicarbonyl compounds in moderate to high yields (up to 95%) with excellent enantioselectivities (up to 95% ee). Based on the configuration of the product and X-ray structure of the catalyst, a possible transition state was proposed to explain the mechanism of the reaction.

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General Procedure for the Asymmetric Mukaiyama Aldol Reaction between Glyoxal Derivative 1a and Enolsilane 3a:
Ligand L7 (0.01 mmol) and Ni(BF4)2˙6H2O (0.01 mmol) were dissolved in CH2Cl2 (0.5 mL) and stirred at 30 ˚C for 1 h. Then the solvent was removed and glyoxal derivative 1a (0.1 mmol) was added. After adding CH2Cl2 (1.0 mL) and enolsilane 3a (0.15 mmol), the mixture was stirred at 30 ˚C for 24 h under N2 atmosphere. Then, THF (2.0 mL) and 1 N HCl (1.0 mL) were added to the reaction mixture. After stirring at r.t. for 30 min, this solution was poured into a separatory funnel and diluted with Et2O (5.0 mL) and H2O (1.0 mL). After mixing, the aqueous layer was discarded and the ether layer was washed with sat. aq NaHCO3 (5.0 mL) and brine (5.0 mL). The resulting ether layer was dried over anhyd MgSO4, and concentrated in vacuo. The crude product was chromatographed on silica gel to give the desired adduct 5a: 94% yield; 92% ee {determined by HPLC analysis with a Chiral OJ-H column, hexane-2-PrOH (80:20), 1.0 mL/min, UV = 254 nm; t R1 = 18.6 min, t R2 = 20.5 min); [α]D ²5 +11.9 (c 0.454, in CH2Cl2}; ¹H NMR (400 MHz, CDCl3): δ = 3.37-3.49 (m, 2 H), 4.04 (d, J = 6.0 Hz, 1 H), 5.68-5.73 (m, 1 H), 7.46-7.55 (m, 4 H), 7.58-7.66 (m, 2 H), 7.95-8.01 (m, 4 H) ppm.