Studies on Direct Stereoselective Aldol Reactions in Aqueous Media

✍ Scribed by Yin-Su Wu; Wei-Yan Shao; Chuan-Qi Zheng; Zhong-Li Huang; Jiwen Cai; Qin-Ying Deng

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: German
• Weight: 124 KB
• Volume: 87
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200490125

✦ Synopsis

Abstract

The direct aldol reaction of 4‐nitrobenzaldehyde catalyzed by NaHCO~3~, with three different ketones, Znproline, NaHCO~3~/Znproline, and L‐proline/Znproline 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 Znproline 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.