Abstract
A chitosan aerogel catalyzed asymmetric aldol reaction of ketones with isatins in the presence of water is described. This protocol was found to be environmentally benign, because it proceeds smoothly in water and the corresponding aldol products were obtained in excellent yields with good enantioselectivities.
Highlights
The 3-substituted-3-hydroxy-2-oxindoles have a stereogenic quaternary center at the C-3 position and a core unit that appears in many natural products and biologically active compounds [1,2,3,4,5,6,7,8].Representative examples are: TMC-95A [9,10], Dioxibrassinine [11,12], SM-130686 [13], 30 - Hydroxygluoisatisin [14], and Convolutamydines (Figure 1) [15]
Asymmetric direct aldol reaction of isatins with ketones [26], we report on the synthesis of oxindoles catalyzed by chitosan aerogel in the presence of water
The direct asymmetric aldol reaction of isatin and hydroxyacetone was selected as a template
Summary
The 3-substituted-3-hydroxy-2-oxindoles have a stereogenic quaternary center at the C-3 position and a core unit that appears in many natural products and biologically active compounds [1,2,3,4,5,6,7,8].Representative examples are: TMC-95A [9,10], Dioxibrassinine [11,12], SM-130686 [13], 30 - Hydroxygluoisatisin [14], and Convolutamydines (Figure 1) [15]. To construct 3-substituted-3-hydroxy-2-oxindoles, asymmetric aldol reaction has been considered one of the most powerful and efficient measures for the formation of carbon–carbon bond at C-3 position [16,17,18,19,20,21] In this context, the asymmetric aldol reaction between isatin and carbonyl compounds has attracted much attention. As a pioneering work in this field, Tomasini and coworkers demonstrated the enantioselective aldol reaction of isatin with acetone catalyzed by a dipeptide-based organocatalyst [22]. Along these lines, Toru et al employed sulfonamides as catalysts for the enantioselective aldol reaction of acetaldehyde with isatin, and successfully achieved the first highly enantioselective crossed-aldol reaction of acetaldehydes with ketones [23]. Zhao et al described the utilization of quinidine thiourea for the highly enantioselective synthesis of
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