66255-92-3Relevant articles and documents
Oxidative cleavage and rearrangement of aryl epoxides using iodosylbenzene: On criegee's trail
Havare, Nizam,Plattner, Dietmar A.
, p. 2036 - 2042 (2012)
Aryl epoxides undergo rearrangement and oxidative cleavage when reacted with in situ prepared hydroxy-λ3-iodane complexes. The presence of H2O plays a decisive role in steering the reaction path. A mechanistic scheme is proposed that accounts for the observed chemoselectivities. Copyright
Biomimetic iron-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide
Gelalcha, Feyissa Gadissa,Anilkumar, Gopinathan,Tse, Man Kin,Brueckner, Angelika,Beller, Matthias
supporting information; experimental part, p. 7687 - 7698 (2009/08/07)
A novel and general biomimetic non-heme Fe-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide is reported herein. The catalyst consists of ferric chloride hexahydrate (FeCl3·OH 2O), pyridine-2,6-dicarboxylic acid (H2-(pydic)), and readily accessible chiral N-arenesulfonyl-N′-benzyl-substituted ethylenediamine ligands. The asymmetric epoxidation of styrenes with this system gave high conversions but poor enantiomeric excesses (ee), whereas larger alkenes gave high conversions and ee values. For the epoxidation of trans-stilbene (1a), the ligands (S,S)-N-(4-toluenesulfonyl)-1,2- diphenylethylenediamine ((S,S)-4a) and its N′-benzylated derivative ((S,S)-5a) gave opposite enantiomers of trans-stilbene oxide, that is, (S,S)-2a and (R,R)-2a, respectively. The enantioselectivity of alkene epoxidation is controlled by steric and electronic factors, although steric effects are more dominant. Preliminary mechanistic studies suggest the in situ formation of several chiral Fe-complexes, such as [FeCl(L*)2-(pydic)] ·HCl (L* = (S,S)-4a or (S,S)-5a in the catalyst mixture), which were identified by ESIMS. A UV/Vis study of the catalyst mixture, which consisted of FeCl3·6H2O, H2(pydic), and (S,S)-4a, suggested the formation of a new species with an absorbance peak at λ = 465 nm upon treatment with hydrogen peroxide. With the aid of two independent spin traps, we could confirm by EPR spectroscopy that the reaction proceeds via radical intermediates. Kinetic studies with deuterated styrenes showed inverse secondary kinetic isotope effects, with values of k H/kD = 0.93 for the β carbon and kH/k D=0.97 for the a carbon, which suggested an unsymmetrical transition state with stepwise O transfer. Competitive epoxidation of para-substituted styrenes revealed a linear dual-parameter Hammett plot with a slope of 1.00. Under standard conditions, epoxidation of la in the presence of ten equivalents of H218O resulted in an absence of the isotopic label in (S,S)-2a. A positive non-linear effect was observed during the epoxidation of la in the presence of (S,S)-5a and (R,R)-5a.
A novel palladium-catalyzed coupling of epoxides with allyl bromide mediated by indium(I) chloride: A cascade epoxide rearrangement-carbonyl allylation
Jiang, Nan,Hu, Qingyuan,Reid, Carrolyn S.,Lu, Yunfeng,Li, Chao-Jun
, p. 2318 - 2319 (2007/10/03)
A cascade epoxide rearrangement-aldehyde allylation was developed by using a combination of InCl and reusable heterogeneous mesoporous silica supported palladium catalysts.
