Oxiranes reactions with hydrogen fluoride

Simple aliphatic oxiranes can be converted to fluorohydrin with hydrogen fluoride only with great difficulty, but the reaction can be carried out in systems with rigid conformations (e.g., steroids, 9,10-epoxydecalin). Good yields can be attained from cyclopentene and cyclohexene oxides with 42% pyridine-polyhydrogen fluoride and in a series of terpene oxides with an amine-hydrogen fluoride complex. ... 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

Vinyloxiranes, when treated with A -bromosuccinimide-triethylamine tris(hydrogen fluoride) at — 10 C in dichloromethane, are converted into the corresponding (bromofluoro-ethyl)oxiranes.43 The regioselectivity and yield of the reaction are dependent on the degree of substitution of the vinyl group. 

Chloromethyl)oxirane (3) affords 1,3-difluoro- and l-chloro-3-fluoropropan-2-ol (4 and 5) on reaction with potassium hydrogen fluoride in diethylene glycol.76 There is no reaction when potassium fluoride is used which indicates that the epoxy ring in 3 is opened by the hydrogen fluoride present in potassium hydrogen fluoride and later the chlorine is exchanged for fluorine. 

The method of choice for adding hydrogen fluoride to oxiranes is the use of boron trifluoride-diethyl ether complex without added hydrogen fluoride. The reaction proceeds with rearrangements to yield the desired fluorohydrins and other byproducts. In some cases the ratio of products depends strongly on the reaction conditions used. 

In most cases, the yields quoted in the literature for the reactions with potassium hydrogen fluoride are not as high. 2-(Hydroxymethyl)oxirane gives 3-fluoropropane-l,2-diol (3) in 26% yield using dimethylformamide as the solvent. ... 

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