Rearranged reactions with hydrogen fluoride

Another example of a simultaneous chlorine-fluorine exchange and rearrangement IS the reaction of orr/io-methylphenylchloroformate with hydrogen fluoride to give a stable tetrafluorobenzodioxtn [34] (equation 25)... 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

In the reaction of a-(trihalomcthyl)sulfanyl ketones with hydrogen fluoride,, -difluoroalkyl fluoridothiocarhonates 14 are obtained instead of the expected trifluoromethyl sulfides.The reaction is thought to proceed via an initial chlorine-fluorine exchange reaction followed by rearrangement into the /i-difluorinated product. 

Reaction of the Westphalen diacetate (555) with hydrogen fluoride afforded the addition product (556) and the rearranged 25-fluoro-D-homo-compound (557), as well as lesser amounts of five other products of rearrangement, three of which were positively identified. Dehydrofluorination of the 9a-fluoro-compound (556) with base gave a mixture of the known 9(10)- and 9(ll)-enes. 

Bock, K. Pedersen, C. Reaction of sugar esters with hydrogen fluoride. XIV. rearrangement of D-xylose and D-lyxose derivatives. Acta Chem. Scand. 1976, B30, 727-732. 

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

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