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Studies on Direct Stereoselective Aldol Reactions in Aqueous Media
Author(s) -
Wu YinSu,
Shao WeiYan,
Zheng ChuanQi,
Huang ZhongLi,
Cai Jiwen,
Deng QinYing
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490125
Subject(s) - chemistry , cyclohexanone , cyclopentanone , aldol reaction , proline , stereoselectivity , diastereomer , aldol condensation , selectivity , catalysis , aqueous solution , aqueous medium , organic chemistry , medicinal chemistry , amino acid , biochemistry
The direct aldol reaction of 4‐nitrobenzaldehyde catalyzed by NaHCO 3 , with three different ketones, Znproline, NaHCO 3 /Znproline, and L ‐proline/Znproline in aqueous media, was studied to explore the selectivity of this environmentally benign type of reaction. Amazingly, NaHCO 3 proper was found to be an efficient catalyst for the selective synthesis of β ‐hydroxy ketones, showing good regio‐ and diastereoselectivity, with all reactions being completed within 9 h. Cyclopentanone and cyclohexanone were found to give rise to reversed diastereoisomer ratios, the syn and anti isomers being the major products, respectively – an unprecedented result. Also, the observed syn diastereoselectivity of aldol reactions catalyzed by L ‐proline and Znproline is remarkable. The corresponding condensation products 7 and 8 were characterized by 1 H‐NMR and single‐crystal X‐ray analyses. Finally, a chelate‐ vs. nonchelate‐type transition state is proposed to account for the differential diastereoselectivities.