Rationally improved chiral Brønsted acid for catalytic enantioselective allylboration of aldehydes with an expanded reagent scope.
Rationally improved chiral Brønsted acid for catalytic enantioselective allylboration of aldehydes with an expanded reagent scope.
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DOI：
10.1021/jo900553f
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发表时间：
2009-05
期刊：
影响因子：
--
通讯作者：
V. Rauniyar;D. Hall
中科院分区：
文献类型：
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作者：
V. Rauniyar;D. Hall
在有机合成中最有用的反应之一，烯丙基金属试剂对羰基化合物的立体控制加成，提供了获得与存在于大量生物活性天然产物和药物中的乙酸酯、丙酸酯和其它含氧官能团相关的对映体富集的高烯丙基醇的途径。在寻找理想的羰基烯丙基化方法的过程中，催化的对映选择性烯丙基硼酸化具有许多优点，例如稳定无毒的烯丙基硼酸频哪醇酯的高化学控制、非对映控制和对映控制。本文报道了一种合理改进的二醇x SnCl（4）配合物作为手性质子酸催化剂，在催化脂肪醛的烯丙基化、甲基烯丙基化、巴豆基化和2-溴烯丙基化反应中提供了前所未有的对映选择性。新的二醇，p-F-Vivol（4 b），使得更活性的二醇x SnCl（4）催化剂能够更有效地与背景的未催化的烯丙基硼化反应竞争。这种优化的催化烯丙基硼化方法的有用性被证明与天然存在的吡喃酮（+）-dodoneine的有效合成和生物学上重要的外亚甲基-γ-内酯的制备。
One of the most useful reactions in organic synthesis, the stereocontrolled addition of allylic metal reagents to carbonyl compounds, provides access to enantiomerically enriched homoallylic alcohols related to the acetate, propionate, and other oxygen-containing functionalities present in a large number of biologically active natural products and pharmaceutical drugs. In the search for an ideal carbonyl allylation methodology, the catalytic enantioselective allylboration presents numerous advantages such as a high chemo-, diastereo-, and enantiocontrol with stable and nontoxic pinacol allylic boronates. This article reports a rationally improved diol x SnCl(4) complex as chiral protic acid catalyst, which provides unprecedented levels of enantioselectivity in the catalytic allylation, methallylation, crotylation, and 2-bromoallylation of aliphatic aldehydes. The new diol, p-F-Vivol (4b), enables a more active diol x SnCl(4) catalyst that can compete more effectively with the background uncatalyzed allylboration. The usefulness of this optimized catalytic allylboration methodology was demonstrated with an efficient synthesis of the naturally occurring pyranone (+)-dodoneine and to the preparation of biologically important exomethylene-gamma-lactones.