Alkenes vicinal difluorides

In the absence of an organic solvent, electrofluorination in neat Et3N 3HF of alkenes like styrene, stilbene, 2,3-dimethylbut-2-ene, or 2-methyl-2-butene yield the corresponding vicinal difluorides in 22 - 55 % yield. Butadiene produces a 1 2 mixture of 1,2- and 1,4- difluorides [5]. 

Phenyl-substituted alkenes with halogen atoms at the double bond react with xenon difluoride in dichloromethane in the presence of hydrogen fluoride forming vicinal difluorides in 50% yield.35... 

Barton and co-workers have studied30 the reactions of trifluoromethyl hypofluorite with various alkenes and found that (Z)- and (T -stilbene give vicinal fluoro trifluoromclhoxy products and vicinal difluorides in chlorotrifluoromethane or diethyl ether, while vicinal fluoro methoxy adducts predominate when the reaction is carried out in methanol at —78 C. svn Addition predominates in all cases on the basis of the fluorination regioselectivity of many alkenes, the formation of a /1-fluoro carbcnium ion is proposed.30... 

The reaction of alkenes 2 in the presence of a nucleophilic species (hydrogen fluoride, methanol, acetic acid) gives vicinal difluorides, methoxy fluorides or acctoxy fluorides in high yield fluorine enters according to the Markovnikov rule.8... 

Fluorine can also be added to alkenes by reaction with a solution of anhydrous hydrogen fluoride in pyridine (Olah s reagent) containing either Af-brotno- or A -iodosuccinimide, or iodine or bromine and silver nitrate. The final addition of silver fluoride to the reaetion mixture leads to the formation of vicinal difluorides 19,23.153... 

The reaction of xenon difluoride with a series of cis- and trans-phenyl substituted alkenes was examined in detail. 1,1-Diphenylethene, l,1-diphenyl-2-fluoroethene and 1.1-diphenyl-propene form vicinal 1,2-difluoro derivatives in 65 95% yield in dichloromethane solution with hydrogen fluoride as the catalyst.29-32 Two possible mechanisms were discussed.33... 

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