Clay-catalyzed Friedel-Crafts alkylation of anisole with dienes

Anisole is alkylated with 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, and 1,3-cyclohexadiene using K10 montmorillonites exchanged with different cations as catalysts in a batch reactor. Brønsted acidity catalyses diene polymerization and favours retro-alkylation. With calcined clays, higher conversions can be reached. Para-monoalkylation is the preferred reaction, whereas the regioselectivity in the diene is controlled by the attack on the least hindered position of the most stable carbenium ion. The catalysts are only partially deactivated under these reaction conditions, and the final yield can be improved to more than 50%, in the case of weak acids, by gradually adding small portions of diene.