Friedel-Crafts alkylation alkyl migration

Lewis acids such as boron trihalides will also form stronger bonds with fluoride than with the other halogens, and can be used to abstract fluoride selectively from halogenated compounds. Some examples of Friedel-Crafts alkylations with fluoro-haloalkanes in which only fluoride is displaced are sketched in Scheme 4.14. As shown by the last example, however, hydride migrations can readily occur under such strongly acidic reaction conditions. 

A single-step benzoylation-oximation has been described on 4-hydroxy-coumarin by the use of PhCCl=NOH and EtjN in boiling methanol. When 7-methoxy-8-prenylcoumarin (osthol) or its epoxide was treated with various Lewis acids, several products were obtained. These resulted from migration or disappearance of the exocyclic double bond, abnormal Friedel-Crafts phenyl-ation, hydration, cyclization, or demethylation. A novel ring-opening of coumarins was effected by treatment with alkyl halides and NaH in THF. The c/5-o-alkoxycinnamic acid was obtained mainly or exclusively. 

At room temperature and slightly above, migration of alkyl substituents on the benzene ring can also occur under Friedel-Crafts conditions ... 

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