Adam Waldemar, Alsters Paul L, Neumann Ronny, Saha-Möller Chantu R, Seebach Dieter, Beck Albert K, Zhang Rui
Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
J Org Chem. 2003 Oct 17;68(21):8222-31. doi: 10.1021/jo034923z.
The epoxidation of allylic alcohols is shown to be efficiently and selectively catalyzed by the oxidatively resistant sandwich-type polyoxometalates, POMs, namely WZnM(2)(ZnW(9)O(34))(2)(-) [M = OV(IV), Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], with organic hydroperoxides as oxygen source. Conspicuous is the fact that the nature of the transition metal M in the central ring of polyoxometalate affects significantly the reactivity, chemoselectivity, regioselectivity, and stereoselectivity of the allylic alcohol epoxidation. For the first time, it is demonstrated that the oxovanadium(IV)-substituted POM, namely ZnW(VO)(2)(ZnW(9)O(34))(2), is a highly chemoselective, regioselective, and also stereoselective catalyst for the clean epoxidation of allylic alcohols. A high enantioselectivity (er values up to 95:5) has been achieved with ZnW(VO)(2)(ZnW(9)O(34))(2)(-) and the sterically demanding TADOOL-derived hydroperoxide TADOOH as regenerative chiral oxygen source. Thus, a POM-catalyzed asymmetric epoxidation of excellent catalytic efficiency (up to 42 000 TON) has been made available for the development of sustainable oxidation processes. The high reactivity and selectivity of this unprecedented oxygen-transfer process are mechanistically rationalized in terms of a peroxy-type vanadium(V) template.
研究表明，抗氧化夹心型多金属氧酸盐（POMs），即WZnM(2)(ZnW(9)O(34))(2)(-) [M = OV(IV)、Mn(II)、Ru(III)、Fe(III)、Pd(II)、Pt(II)、Zn(II)；q = 10 - 12]，能以有机氢过氧化物作为氧源，高效且选择性地催化烯丙醇的环氧化反应。值得注意的是，多金属氧酸盐中心环中过渡金属M的性质对烯丙醇环氧化反应的反应活性、化学选择性、区域选择性和立体选择性有显著影响。首次证明，氧钒(IV)取代的POM，即ZnW(VO)(2)(ZnW(9)O(34))(2)，是烯丙醇清洁环氧化反应的高化学选择性、区域选择性和立体选择性催化剂。使用ZnW(VO)(2)(ZnW(9)O(34))(2)(-)和空间位阻较大的TADOOL衍生氢过氧化物TADOOH作为可再生手性氧源，已实现了高对映选择性（对映体比例高达95:5）。因此，一种具有优异催化效率（高达42000 TON）的POM催化不对称环氧化反应可用于可持续氧化过程的开发。根据过氧型钒(V)模板，从机理上合理解释了这一前所未有的氧转移过程的高反应活性和选择性。
