Fluoroketones, formation

The regioselectivity in oxetane formation is probably determined primarily by the orientation of the CT complexes. Additions of a-fluoroketones, which have such low reduction potentials as to be particularly hot 132> and therefore potentially unselective acceptors, do proceed with negligible regioselectivity 126>. The actual product ratio is quite complex kinetically because of all the various competing reactions of four separate intermediates. 

A fluorous medium has been utilized for alkcnc epoxidation employing the dioxirane derived from the fluoroketone 14, which is also effective in catalytic quantities with Oxone as the terminal oxidant. For example, treatment of tro w-4-decene (13) with 5 mol% of ketone 14 and 1.5 equiv of Oxone in a bicarbonate buffered water exanuoroisopropanol (HFIP) medium led to the quantitative formation of the corre.sponding epoxide 15 <01TL4463>. 

Nucleophilic attack by cyanide ion (NaCN in MeCN) on hexafluoro-acetone (2 equiv.) leads to the formation of 2,2,5,5,-tetrakis(trifluoromethyl)-4-oxazolidinone (Scheme 38 R p, R f = CF )/ and this reaction has been extended to other fluoroketones (see Table 3) to provide fluorinated 4-... 

A second class of catalysts comprises perfluorinated ketones such as hexafluoro-acetone [38] and perfluoro-2-octanone ]39]. This class of catalyst is assumed to reversibly form peroxyhemihydrates when exposed to hydrogen peroxide ]40] the latter are the active oxygen-transfer agents. Oxygen transfer to the substrate is accompanied by formation of the ketone s hydrate, which, in equilibrium, regenerates the fluoroketone catalyst. 

One electron oxidation of silyl enol ether 44 leads to the formation of a radical ion pair of 45 and the xenon difluoride radical anion. Subsequent transfer of a fluoride radical yields cation 46, which reacts by loss of the trimethylsilyl cation to yield the fluoroketone 47. The formation of ketone 49 is explained by a [1,5] -hydrogen migration from the trimethylsilyl group to the radical cationic moiety of 45, leading to the formation of 48. 

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