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首页> 外文期刊>Chemistry: A European journal >Highly enantioselective epoxidation of 2-methylnaphthoquinone (vitamin K-3) mediated by new Cinchona alkaloid phase-transfer catalysts
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Highly enantioselective epoxidation of 2-methylnaphthoquinone (vitamin K-3) mediated by new Cinchona alkaloid phase-transfer catalysts

机译：新的金鸡纳生物碱相转移催化剂介导的2-甲基萘醌（维生素K-3）的高度对映选择性环氧化

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摘要

In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target. With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chiratity through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles. For example, the well-established 9-anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[(1,8-S;4,5-R)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-di-methanoanthracene. The asymmetric epoxidation of vitamin K-3 was used as the test reaction for our novel PTCs. The readily available PTC 10 (derived from quinine in three convenient and high-yielding steps) proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2.50 mol %, the quinone epoxide was obtained in 76 % yield and with 85 % ee (previously: <= 34% ee), using commercial bleach (aqueous sodium hypochlorite) as the oxidant. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted. Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained.
机译：在催化不对称环氧化领域，环状烯酮和醌的高对映选择性转化是一个极富挑战性的目标。为了开发用于此目的的新型高效相转移催化剂，我们进行了基于奎宁和奎尼丁的PTC的系统结构变化。在总共15种新的季铵PTC中，修饰包括例如将奎宁甲氧基交换为游离羟基或其他烷氧基取代基，以及通过手性生物碱奎宁环氮原子的烷基化引入其他手性元素亲电试剂。例如，将成熟的9-蒽烯基甲基换成9-氯甲基-[（1,8-S; 4,5-R）-1,2,3,4， 5,6,7,8-八氢-1,4：5,8-二-甲基蒽。维生素K-3的不对称环氧化被用作我们新型PTC的测试反应。事实证明，现成的PTC 10（在三个便捷且高产率的步骤中由奎宁衍生而来）是迄今为止已知的对映选择性最高的催化剂：在催化剂负载量仅为2.50 mol％的情况下，苯醌环氧化物的收率为76％。使用市售漂白剂（次氯酸钠水溶液）作为氧化剂，收率可达85％ee（以前：<= 34％ee）。为了合理化我们的新型相转移催化剂的感应效果，对中间氯氧基烯醇盐-PTC离子对中的空间相互作用进行了计算分析。基于此分析，可以一致地解释所有15种新颖PTC的感应感。

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