Trifluoromethyl-substituted epoxides

The aerobic epoxidation of j0-trifluoromethyl-, -disubstimted enones, catalysed by cinchona alkaloid (73), in methyl t-butyl ether under air in the presence of CS2CO3 and methylhydrazine affords enantiomerically enriched trifluoromethyl-substituted epoxides in excellent yields and up to 96-99% ee. 0-labeling experiments suggest a mechanism involving the activation of molecular oxygen." ... 

The other main group elements which form peroxo complexes are d6 and d8 systems in group VIII including iridium, palladium and platinum. The ji-peroxo complexes do not generally catalyse the epoxidation of olefins with hydrogen peroxide,95,96 but it has been found that trifluoromethyl-substituted Pd(II) and Pt(II) hydroperoxides will perform such a transformation.97... 

Analogous to epoxides, aziridines can be prepared by the methylenation of imines. In this case, ethyl diazoacetate is the most common source of carbenes. For example, the imine derived from p-chlorobenzaldehyde 148 is converted to the c/j-aziridinyl ester 149 upon treatment with ethyl diazoacetate in the presence of lithium perchlorate <03TL5275>. These conditions have also been applied to a reaction medium of the ionic liquid l-n-butyl-3-methylimidazolium hexafluorophosphate (bmimPFe) with excellent results <03TL2409>. An interesting enantioselective twist to this protocol has been reported, in which a diazoacetate derived from (TJ)-pantolactone 150 is used. This system was applied to the aziridination of trifluoromethyl-substituted aldimines, which were prepared in situ from the corresponding aminals under the catalysis of boron trifluoride etherate <03TL4011>. 

Aryl selenium compounds also form adducts with hydrogen peroxide, ArSe (O)OOH, that are able to carry out epoxidation [188,189], albeit at low rates [190,191]. Improvements can be made by substitution of the aromatic ring with electron-withdrawing trifluoromethyl groups [192], for example, to form the lizs-[3,5-Ws-(trifluoromethyl)phenyl]diselenide. 

It has recently been shown that an a-trifluoromethyl epoxide, (S) -103, can be de-protonated, the electron-withdrawing effect of the trifluoromethyl group promoting formation (and stabiHsation) of the intermediate hthiated epoxide 104, which can subsequently be trapped with a range of electrophiles carbonyl, triphenylsilyl, triphenyltin and methyl compoimds (Scheme 20) [72]. lithia-tion-substitution proceeds without loss of configuration. 

Several primary and secondary amines have been used in the 5 2 ring opening of 2,8-bis(trifluoromethyl)quinoline-4-oxirane at the least-substituted carbon of the epoxide, giving possible antimalarial dmgs. Yields range from 35 to 98% with... 

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