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Crossed aldol reaction using cross-linked polymer-bound lithium dialkylamide

Atsushi Seki, Fusae Ishiwata, Youichi Takizawa and Masatoshi Asami*

*Department of Advanced Materials Chemistry, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan, Email: m-asamiynu.ac.jp

A. Seki, F. Ishiwata, Y. Takizawa, M. Asami, Tetrahedron, 2004, 60, 5001-5011.

DOI: 10.1016/j.tet.2004.04.026


Abstract

Reusable polymer-bound lithium dialkylamides were employed in crossed aldol reaction of various carbonyl compounds with aldehydes to afford the corresponding β-hydroxycarbonyl compounds. The introduction of spacer chains between the base moiety and the polystyrene backbone increased the yields of the desired aldol adducts.

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Details

The study explores the use of cross-linked polymer-bound lithium dialkylamides in crossed aldol reactions to produce β-hydroxycarbonyl compounds. The introduction of spacer chains between the base moiety and the polystyrene backbone significantly improved the yields of aldol adducts. These polymer-bound reagents sometimes outperformed lithium diisopropylamide (LDA) under homogeneous conditions. The polymeric reagents demonstrated consistent efficiency upon repeated use. The research detailed the synthesis of various polymer-bound lithium dialkylamides and their application in aldol reactions involving ketones, esters, and amides with aldehydes. Spacer-modified polymers, particularly those with a pentamethylene spacer, showed enhanced reactivity and selectivity. The study also highlighted the successful generation of enolates from methyl ketones and propionic acid esters, leading to high yields and good regioselectivity. The polymer-bound reagents were easily recoverable and reusable, maintaining their efficiency over multiple cycles. The findings suggest that these polymer-bound lithium dialkylamides, especially with appropriate spacers, are effective and reusable alternatives to traditional bases like LDA in aldol reactions, offering higher selectivity and comparable yields.


Key Words

Supported reagents, Lithium dialkylamides, Aldol reaction, Aldol-Addition, β-Hydroxycarbonyl compounds, β-Hydroxycarboxylic compounds, Deprotonation, Lithium enolates


ID: J72-Y2004-480