PROCEDURE FOR THE CATALYTIC ASYMMETRIC EPOXIDATION OF ALLYLIC ALCOHOLS IN THE PRESENCE OF MOLECULAR-SIEVES
PROCEDURE FOR THE CATALYTIC ASYMMETRIC EPOXIDATION OF ALLYLIC ALCOHOLS IN THE PRESENCE OF MOLECULAR-SIEVES
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DOI：
10.1021/jo00360a058
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发表时间：
1986-05-16
影响因子：
3.6
通讯作者：
SHARPLESS, KB
中科院分区：
文献类型：
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作者：
HANSON, RM;SHARPLESS, KB
在最初关于钛催化烯丙醇不对称环氧化反应的报告1中，一般程序要求酒石酸钛“催化剂”的化学计量量。该报告还提到，10%的催化剂足以反应底物，最近的(E)-2-己烯-l-醇的不对称环氧化过程规定了50%的催化剂。然而，迄今为止，不对称环氧化的许多应用几乎都是通过使用化学计量或接近化学计量量的酒石酸钛催化剂来进行的。我们现在报告了采用过氧化氢叔丁基（thbhp）和催化（即< 10%）量的钛（IV）异丙醇和酒石酸二乙酯对丙烯醇进行不对称环氧化的第一个一般程序。这种改性的关键因素是在反应过程中存在3A或4A分子筛（沸石）。使用催化量的钛的优点包括经济、条件温和、易于分离、产量增加以及产品原位衍生化的潜力。在没有分子筛的情况下，仅使用5 mol%的钛（IV）异丙醇的反应通常会产生低光学纯度（39-80% ee），反应进行缓慢，通常在转化率达到50-60%后停止。相比之下，我们的新方法使反应仅使用5-10 mol%的钛（IV）异丙醇和6-13 mol%的酒石酸酯，以类似于化学计量系统的速率获得高对映选择性（90-95% ee）的产物。下面介绍的两种方法（一种用于二取代烯丙醇，另一种用于三取代烯丙醇）非常相似，只是在反应条件和分离技术的微小细节上有所不同。
In the original report1 on the titanium-catalyzed asym-metric epoxidation of allylic alcohols, the general procedure called for a stoichiometric amount of the titanium tartrate “catalyst”. That report also mentioned that 10% catalyst sufficed for reactive substrates, and a recent procedure2 for the asymmetric epoxidation of (E)-2-hexen-l-ol prescribed 50% catalyst. Nevertheless, the numerous ap-plications of the asymmetric epoxidation to date have been carried out almost exclusively by using stoichiometric or near-stoichiometric amounts of the titanium-tartrate catalyst. 3We now report the first general procedure for the asymmetric epoxidation ofallylic alcohols employing tert-butyl hydroperoxide (TBHP) and catalytic (ie,< 10%) amounts of titanium (IV) isopropoxide and diethyl tartrate. The key element of this modification is the presence of 3A or 4A molecular sieves (zeolites) during the reaction. The advantages of using a catalytic amount of titanium include economy, mildness of conditions, ease of isolation, increased yields, and the potential for in situ derivatization of the product. In the absence of molecular sieves, reactions employing only 5 mol% titanium (IV) isopropoxide often yield product of low optical purity (39-80% ee), proceed slowly, and generally stop after achieving only 50-60% conversion. In contrast, our new procedure enables the reaction to be carried out by using only 5-10 mol% titanium (IV) isopropoxide and only 6-13 mol% of tartrate ester, giving product of high enantioselectivity (90-95% ee) at rates similar to those of the stoichiometric system. The two procedures presented below (one for disubstituted allylic alcohols and one for trisubstituted allylic alchols) are very similar and differ only in minor details of the reaction conditions and iso-lation technique.