Friedel–Crafts reactions in ionic liquids: the counter-ion effect on the dealkylation and acylation of methyl dehydroabietate

Ionic liquids with different counter-ion and alkyl substitutes were tested as solvents in the dealkylation and acylation of methyl dehydroabietate, a useful and inexpensive building block for the synthesis of higher diterpenes derivatives. Ionic liquids with halogen counter-ions are very active in both reactions with high rate constant and conversion, avoiding the use of the conventional solvents (benzene and carbon disulfide) in these reactions. In the dealkylation reaction, the change of counter-ion from halogens to tetrafluoroborate had a dramatic effect on the stereoselectivity, showing the importance of the counter-ion in the course of the reactions.