Fluorination with xenon difluoride. Reaction with halogenated hydrocarbons

Filler and coworkers 1-5] have demonstrated the utility of xenon difluoride as a selective fluorinating agent for aromatic hydrocarbons in the liquid phase, while Mackenzie and coworker 6] have fluorinated aromatic compounds in the vapour phase. We have developed a fluorination reaction of phenyl substituted olefins resulting in high yields of vicinal difluorides 7,8] and trifluoroacetates, depending on the catalyst. In our continued interest in the use of xenon difluoride as a mild fluorinating agent for fluorination of organic compounds, we have tries to fluorinate some heterocyclic ring systems, e.g. imidazo-(1,2-b)-pyridazine, under conditions similar of those used for fluorination of phenyl substituted olefins 7,8,9] (room temperature, methylene chloride as solvent, hydrogen fluoride as catalyst). It is well known that heteroaromatic compounds are less reactive toward electrophilic substitution reactions then aromatic hydrocarbon systems. However, it has been shown that bromination of imidazo-(1,2-b) -pyridazine results in 3-bromo products 10], while in chlorination with phosphorus pentachloride 11], the entering order of chlorine atoms is at position 3 > 2, 7 > 8 > 6 (Radical reactions).