Studies on the Synthesis of Squaric Acid Ephedrine and Their Application in Asymmetric Catalytic Borane Reduction of Prochiral Ketones

Chem. J. Chinese Universities ›› 2001, Vol. 22 ›› Issue (11): 1846.

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Studies on the Synthesis of Squaric Acid Ephedrine and Their Application in Asymmetric Catalytic Borane Reduction of Prochiral Ketones

L Shou-Mao^1,2, ZHOU Hai-Bing¹, ZHANG Ji¹, XIE Ru-Gang³, ZHOU Zhong-Yuan³, CHAN Albert-S.C.⁴

1. Department of Chemistry, Sichuan University, Chengdu 610064, China;
2. Department of Chemistry, Xianning Teachers College, Xianning 437000, China;
3. Department of Applied Biologyand Chemical Technology, The Hong Kong Polytechnic University, Hong Kong, China;
4. Department of Chemistry, National Chung-Hsing University, Taichung, China

Received:2000-11-17 Online:2001-11-24 Published:2001-11-24

Abstract

Abstract: Seven squaric acid ester amides or squaric acid diamides have been conveniently prepared by the reaction of natural ephedrine and squaric acid diesters, in which the later can be sythesized by refluxing squaric acid in the corresponding alcohols. When squaric acid amide ester 4a reacted with alkyl amines or was treated with aqueous sodium hydrosulfide, the new ligands which contain nitrogen or sulfur atom at C₃ of squaric acid were obtained. Five ligands were synthesized for the first time. The chiral oxazaborolidines formed in situ have been used in the enantioselective borane reduction of prochiral ketones and diketones to afford the alcohols in the range 85%-98% yields and 52.5%-87.4% enantiomeric excess respectively. All new ligand structures were comfirmed by IR,¹H NMR, MSand elemental analysis, the crystal structure of compound 4b was lerrified by X-ray diffraction.

Key words: Squaric ephedrine amide, Chiral oxazaborolidines, Asymmetric catalysis, Reduction of aryl ketones

CLC Number:

O622.6

TrendMD:

L� Shou-Mao, ZHOU Hai-Bing, ZHANG Ji, XIE Ru-Gang, ZHOU Zhong-Yuan, CHAN Albert-S.C., YANG Deng-Kuei . Studies on the Synthesis of Squaric Acid Ephedrine and Their Application in Asymmetric Catalytic Borane Reduction of Prochiral Ketones[J]. Chem. J. Chinese Universities, 2001, 22(11): 1846.

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Studies on the Synthesis of Squaric Acid Ephedrine and Their Application in Asymmetric Catalytic Borane Reduction of Prochiral Ketones

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