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Synlett 2005(12): 1873-1876  
DOI: 10.1055/s-2005-871559
LETTER
© Georg Thieme Verlag Stuttgart · New York

Asymmetric Alkylation of a tert-Butyl Benzophenone Schiff Base Derivative in Water

Le Lia, Zhengpu Zhang*a, Xiaoxia Zhu*a,b, A. Popac, Shanwei Wanga
a Key Laboratory of Functional Materials for Adsorption and Separation, Institute of Polymer Chemistry, Nankai University, Tianjin 300071, P. R. China
b Département de Chimie, Université de Montréal, C. P. 6128, Succursale Centre-ville, Montréal, QC, H3C 3J7, Canada
c Institutul de Chimie Timisoara, Blvd Mihai Viteazul nr. 24, 1900-Timisoara, Romania
Fax: 86(22)23503510; e-Mail: zhangzp@nankai.edu.cn; e-Mail: julian.zhu@umontreal.ca;
Further Information

Publication History

Received 18 May 2005
Publication Date:
22 June 2005 (online)

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Abstract

The asymmetric alkylation of a tert-butyl benzophenone Schiff base derivative in water has been successfully carried out in a ‘reversed-phase reaction’. The effects of chiral phase-transfer catalysts (PTCs), electrophiles, and reaction conditions (temperature, concentration, and the ratio of reagents, etc.) were investigated. ­Under the optimized conditions high chemical yield (99%) and good ee (up to 87%) were obtained.

Key words

alkylations - phase-transfer - asymmetric catalysis - ­cinchona alkoloids - amino acids

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Typical procedure for asymmetric alkylation: A mixture of 1 (0.678 mmol, 200 mg), benzyl bromide (5.0 equiv, 0.4 mL) and the catalyst (0.01 equiv, 4 mg) was cooled to 5 °C and a 1 M KOH aqueous solution (13 equiv, 9.0 mL) was added. The mixture was vigorously stirred. When the reaction was finished, the mixture was extracted with ethyl acetate (4 × 20 mL). The organic extracts were combined and dried (Na2SO4) then evaporated in vacuo.

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Synthesis of catalyst 3: Cinchonidine (11.0 mmol, 3.234 g) and 4,4′-chloromethyl biphenyl (5.0 mmol, 1.255 g) were added to the solution of EtOH-DMF-CHCl3 (2.5: 3:1, 26 mL), followed by stirring at 100 °C for 8 h. After cooling the reaction mixture to room temperature, the resulting suspension precipitated by the addition of Et2O. The solids were filtered, washed with Et2O. The crude solid was recrystallized from MeOH to afford the desired product 3.566 g (85% yields) as an orange solid. The structure of sample was confirmed by a range of analytical methods.

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Synthesis of catalyst 4: A styrene-divinylbenzene copolymer (4.5 g, 7%) was swollen in DMF (100 mL) for 2 h, 9-O-(4-nitrobenzoyl)cinchonine (11.6 g) was added. The flask was heated at 80 °C for 60 h. During the course of the reaction the color of the copolymer beads turned dark red. After cooling, the polymer beads were separated by filtration, washed with EtOH (3 × 20 mL), DCE (3 × 20 mL), Et2O (3 × 20 mL), and dried in vacuo. The structure of the sample was certified by several analytical methods.