CATALYTIC ASYMMETRIC EPOXIDATION AND KINETIC RESOLUTION - MODIFIED PROCEDURES INCLUDING INSITU DERIVATIZATION
CATALYTIC ASYMMETRIC EPOXIDATION AND KINETIC RESOLUTION - MODIFIED PROCEDURES INCLUDING INSITU DERIVATIZATION
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DOI：
10.1021/ja00253a032
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发表时间：
1987-09-16
影响因子：
15
通讯作者：
SHARPLESS, KB
中科院分区：
文献类型：
--
作者：
GAO, Y;HANSON, RM;SHARPLESS, KB
3A或4A分子筛（沸石）的使用显著增加了钛（IV）催化的伯烯丙醇的不对称环氧化的范围。而在没有分子筛的情况下，仅使用5 - 10摩尔% Ti（O-i-Pr）4的环氧化通常导致低转化率或低对映选择性，在分子筛存在下，这样的反应通常导致高转化率（> 95%）和高对映选择性（90- 95%ee）。报道了20种烯丙基伯醇的环氧化反应。特别值得注意的是肉桂醇、2-十四烷基-2-丙烯-1-醇、烯丙醇和巴豆醇化合物的环氧化，这些化合物迄今为止被认为是不对称环氧化的困难底物。在烯丙醇的情况下，即使在不存在分子筛的情况下，使用氢过氧化枯烯也显著提高了反应速率和转化率。通常，相对于使用50-100摩尔% Ti（0-t-Pr）4的反应，对映选择性略微降低（降低1- 5%ee）。低分子量烯丙醇的环氧化特别容易，并且与原位衍生化结合，提供了许多以前难以获得的环氧醇双酮的合成。还描述了用10 mol% Ti（0-f-Pr）4对4种仲烯丙醇的动力学拆分。讨论了分子筛在反应中的作用以及反应化学计量比、氧化剂和酒石酸盐的变化对反应的影响，介绍了1980年在Ti（0-/-Pr）4和酒石酸二乙酯（DET）存在下烯丙醇与叔丁基过氧化氢（TBHP）反应生成高对映体纯度的环氧醇（方案I）。[1]从那时起，人们对这种不对称环氧化过程有了很多了解。一些评论已经出版，2和两篇论文从这些实验室已处理的反应机理方面。3· 4最初描述的环氧化反应使用化学计量量的催化剂，尽管如原始报告的一个脚注中所述，某些底物的反应可以用少至10%的催化剂进行，对映选择性损失很小，产率有所增加。
The use of 3A or 4A molecular sieves (zeolites) substantially increases the scope of the titanium (IV)-catalyzed asymmetric epoxidation of primary allylic alcohols. Whereas without molecular sieves epoxidations employing only 5 to 10 mol% Ti (0-/-Pr) 4 generally lead to low conversion or low enantioselectivity, in the presence of molecular sieves such reactions generally leadto high conversion (> 95%) and high enantioselectivity (90-95% ee). The epoxidations of 20 primary allylic alcohols are described. Especially noteworthy are the epoxidations of cinnamylalcohol, 2-tetradecyl-2-propen-1-ol, allyl alcohol, and crotyl alcohol—compounds which heretoforehad been considered difficult substrates for asymmetric epoxidation. In the case of allyl alcohol, the use of cumene hydroperoxide substantially increases both the reaction rate and the conversion, even in the absence of molecular sieves. In general, enantioselectivities are slightly depressed (by 1-5% ee) relative to reactions employing 50-100 mol% Ti (0-t-Pr) 4. The epoxidation of low molecular weightallylic alcohols is especially facilitated and, in conjunction with in situ derivatization, provides for the synthesis of many epoxy alcohol synthons which were previously difficult to obtain. The kinetic resolution of four secondary allylic alcohols with 10 mol% Ti (0-f-Pr) 4 is also described. The role of molecular sieves in the reaction and the effects of variation in reaction stoichiometry, oxidant, and tartrate are discussed.The reaction of an allylic alcohol with iert-butyl hydroperoxide (TBHP) in the presence of Ti (0-/-Pr) 4 and diethyl tartrate (DET) to form an epoxy alcohol of high enantiomeric purity was intro-duced in 1980 (Scheme I). 1 Since then, much has been learned about this asymmetric epoxidation process. Several reviews have been published, 2 and two theses from these laboratories have dealt with mechanistic aspects of the reaction. 3· 4 The epoxidation as initially described employs a stoichiometric amount of catalyst, even though, as noted in one of the footnotes to the original report, reactions of certain substrates can be carried out with as little as 10% catalyst with little loss of enantioselectivity and some increase in yield.