An efficient asymmetric epoxidation method for trans-olefins mediated by a fructose-derived ketone
An efficient asymmetric epoxidation method for trans-olefins mediated by a fructose-derived ketone
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DOI：
10.1021/ja962345g
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发表时间：
1996-10-09
影响因子：
15
通讯作者：
Shi, Y
中科院分区：
文献类型：
--
作者：
Tu, Y;Wang, ZX;Shi, Y
环氧化物是合成对映体纯复杂分子的重要手性组成部分。烯烃的不对称环氧化反应为合成对映体富集的环氧化物提供了强有力的策略。烯丙醇和未官能化的顺式烯烃的环氧化反应取得了巨大的成功。然而，不含高对映体过量烯丙醇基的反式烯烃的环氧化反应仍然是一个具有挑战性的问题。4 .最好探讨其他解决办法。在许多其他有效的烯烃环氧化方法中，5 -二氧环烷是非常通用的氧化试剂，它们作为环氧化试剂的用途已经特别突出。反应迅速，只需简单的检查。与二氧环烷相关的一个重要特征是，它们可以由氧酮（过氧单硫酸氢钾）和酮原位生成，8这为使用手性酮时不对称环氧化提供了机会。然而，在二氧环烷介导的不对称环氧化领域的进展有限。9对映体过量（ee）很低（9-20%）。由于二氧环烷有两个反应位点，限制可能的竞争方法是至关重要的。最近，在这方面取得了一些进展。Yang报道了一个有趣的C2对称环手性酮用于不对称环氧化。10在一个病例中获得了87%的ee，尽管大多数病例的ee值很低（5-50%）。在此，我们希望报告我们在不对称环氧化领域的努力。我们所使用的酮具有以下一般特征：(1)立体中心靠近反应中心，使底物与催化剂之间具有有效的立体化学通讯；(2)羰基上的熔环和季中心R的存在使立体中心的外映化最小化；(3)对催化剂的一面进行位阻，以限制可能的竞争途径。酮3具有这些理想的结构特征，并且很容易由非常便宜的d -果糖（15美元/公斤）通过丙酮，HClO4, 0℃，53%)的酮化和氧化（PCC, rt, 93%）制备。11
Epoxides are very important chiral building blocks for the synthesis of enantiomerically pure complex molecules. 1 Asymmetric epoxidation of olefins presents a powerful strategy for the synthesis of enantiomerically enriched epoxides. Great success has been achieved in the epoxidation of allylic alcohols2 and unfuctionalized cis-olefins. 3 However, the epoxidation of trans-olefins bearing no allylic alcohol group with high enantiomeric excess still remains a challenging problem. 4 It was desirable to explore alternative systems for a solution. Among many other powerful methods for the epoxidation of olefins, 5 dioxiranes are remarkably versatile oxidation reagents, and their use as epoxidation reagents has risen to particular prominence. 6, 7 The reaction is rapid and requires a simple workup. An important feature associated with dioxiranes is that they can be generated in situ from Oxone (potassium peroxomonosulfate) and a ketone, 8 which provides opportunities for asymmetric epoxidation when a chiral ketone is used. However, progress in the area of dioxirane-mediated asymmetric epoxidation has been limited. 9 The enantiomeric excess (ee) has been low (9-20%). Since dioxiranes have two reacting sites, it is crucial to limit possible competing approaches. Recently, some progress has been made in this regard. Yang reported an intriguing C2 symmetric cyclic chiral ketone for asymmetric epoxidation. 10 An 87% ee was obtained in one case, although the ee values for most cases were low (5-50%). Herein we wish to report our efforts in the area of asymmetric epoxidation. We are utilizing ketones containing the following general features:(1) the stereogenic centers are close to the reacting center, resulting in efficient stereochemical communication between substrates and the catalyst;(2) the presence of a fused ring and a quaternary center R to the carbonyl group minimizes the epimerization of the stereogenic centers;(3) one face of the catalyst is sterically blocked to limit the possible competing approaches. Ketone 3 has these desirable structural features, and is readily prepared from very inexpensive D-fructose ($15/kg) by ketalization (acetone, HClO4, 0 C, 53%) and oxidation (PCC, rt, 93%). 11