Chi Yonggui, Scroggins Steven T, Boz Emine, Fréchet Jean M J
Division of Materials Sciences, Lawrence Berkeley National Laboratory and College of Chemistry, University of California, Berkeley, California 94720-1460, USA.
J Am Chem Soc. 2008 Dec 24;130(51):17287-9. doi: 10.1021/ja806584q.
A fundamental chemoselectivity challenge that remains intrinsically unsolved in aldol-type reactions is the suppression of self-aldol reactions with enolizable aldehydes in reactions such as cross-aldol processes. Contrasting with the usual practice of using large excesses of one component to compete with the undesired self-aldehyde condensation reactions, we have developed an enzyme-like polymer catalyst consisting of a hyperbranched polyethyleneimine derivative and proline that can eliminate the self-aldol reactions by suppressing an irreversible aldol condensation pathway. Control experiments and preliminary mechanistic studies suggest that the polymer catalyst provides an optimum environment for the aldol reaction to proceed selectively in water, and the catalytic conditions provided by the polymer are difficult to duplicate with typical small molecule analogues. This polymer catalyst system or its modified version has potential applications in developing a new or more efficient synthesis, as demonstrated in a dynamic catalytic process for the preparation of alpha,beta-unsaturated ketones using cross ketone/aldehyde reactions without the need for excess substrates.
在羟醛型反应中，一个本质上仍未解决的基本化学选择性挑战是，在诸如交叉羟醛反应等反应中，抑制可烯醇化醛的自身羟醛反应。与使用大量过量的一种组分来与不希望的自身醛缩合反应竞争的通常做法不同，我们开发了一种由超支化聚乙烯亚胺衍生物和脯氨酸组成的类酶聚合物催化剂，该催化剂可以通过抑制不可逆的羟醛缩合途径来消除自身羟醛反应。对照实验和初步机理研究表明，该聚合物催化剂为羟醛反应在水中选择性进行提供了最佳环境，并且该聚合物提供的催化条件很难用典型的小分子类似物来复制。这种聚合物催化剂体系或其改性版本在开发新的或更有效的合成方法方面具有潜在应用，如在使用交叉酮/醛反应制备α,β-不饱和酮的动态催化过程中所展示的那样，该过程无需过量底物。
