Highly Enantioselective Epoxidation of 2-Methylnaphthoquinone (Vitamin K3) Mediated by NewCinchona Alkaloid Phase-Transfer Catalysts
作者:Albrecht Berkessel、Maria Guixà、Friederike Schmidt、Jörg M. Neudörfl、Johann Lex
DOI:10.1002/chem.200600993
日期:2007.5.25
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
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具挑战性的目标。为了开发用于此目的的新型高效相转移催化剂,我们对基于奎宁和奎尼丁的PTC进行了系统的结构变化。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,以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(在三个方便且高产率的三个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:≤或= 34%ee)。为了合理化我