A Highly Chemoselective, Diastereoselective, and Regioselective Epoxidation of Chiral Allylic Alcohols with Hydrogen Peroxide, Catalyzed by Sandwich-Type Polyoxometalates: Enhancement of Reactivity and Control of Selectivity by the Hydroxy Group through Metal−Alcoholate Bonding
作者:Waldemar Adam、Paul L. Alsters、Ronny Neumann、Chantu R. Saha-Möller、Dorit Sloboda-Rozner、Rui Zhang
DOI:10.1021/jo0266386
日期:2003.3.1
Sandwich-type polyoxometalates (POMs), namely [WZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], are shown to catalyze selectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide under mild conditions (ca. 20 degrees C) in an aqueous/organic biphasic system. The transition metals M in the central ring of polyoxometalate do not affect the reactivity
三明治型多金属氧酸盐(POM),即[WZnM2(ZnW9O34)2] q- [M = Mn(II),Ru(III),Fe(III),Pd(II),Pt(II),Zn(II) ; q = 10-12],表明在温和条件下(约20摄氏度)在水/有机双相体系中,用30%过氧化氢选择性催化手性烯丙醇的环氧化。多金属氧酸盐中心环中的过渡金属M不影响过氧化氢使烯丙醇环氧化的反应性,化学选择性或立体选择性。对于空洞的Keggin POM [PW11O39] 7-,可以观察到相似的选择性,尽管产物收率明显降低,其中过氧钨酸盐络合物已被证明是活性氧化物质。所有这些特征都支持钨过氧配合物,而不是高价过渡金属氧物种作为三明治型POM催化环氧化的关键中间体。通过乙酰化或甲基化将羟基官能团封端时,这些POM未观察到这些羟基保护的底物[1a(Ac)和1a(Me)]的反应性。提出了一种模板来说明反应性和选择性的显着提高,