Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable
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 allylicalcohols 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
Stereoselective expoxidation of allylic and homoallylic alcohols with 30% hydrogen peroxide catalyzed by tungstic acid in buffered media
作者:Denis Prat、Bernard Delpech、Robert Lett
DOI:10.1016/s0040-4039(00)84080-0
日期:1986.1
The aqueous tungstic acid-catalyzed hydrogenperoxideepoxidation of allylicalcohols affords the same major diastereoisomer as the VO(acac)2/tBuOOH system with quite comparable stereoselectivities. In contrast, epoxidation of homoallylic alcohols appears to be much less stereoselective.
Chiral Hydroperoxides as Oxygen Source in the Catalytic Stereoselective Epoxidation of Allylic Alcohols by Sandwich-Type Polyoxometalates: Control of Enantioselectivity through a Metal-Coordinated Template
作者:Waldemar Adam、Paul L. Alsters、Ronny Neumann、Chantu R. Saha-Möller、Dieter Seebach、Albert K. Beck、Rui Zhang
DOI:10.1021/jo034923z
日期:2003.10.1
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)](q)(-) [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
Mechanism of Chorismate Mutase: Contribution of Conformational Restriction to Catalysis in the Claisen Rearrangement
作者:Nikolai A. Khanjin、James P. Snyder、F. M. Menger
DOI:10.1021/ja992453d
日期:1999.12.1
The mechanism of the enzyme- and antibody-catalyzed Claisenrearrangement of chorismate to prephenate was investigated experimentally on model compounds and by using quantum chemistry calculations at the Becke3LYP/6-31G* level of theory. Conformational restriction of the allyl vinyl ether fragment to the reactive chairlike conformation in 1 induces a 2 × 105-fold rate acceleration (ΔΔG⧧ = 7.3 kcal/mol)