Acidity effect in the regiochemical control of the alkylation of phenol with alkenes

Abstract

Treatment of 1∶1 mixtures of phenol and linear alkenes in the presence of an acidic promoter in CHCl₃ at room temperature results in ortho-regioselective monoalkylation producing sec-alkylphenols in 48–60% yield. In similar reactions, branched alkenes lead exclusively to the corresponding para-tert-alkylphenols in 80–85% yield. Addition of increasing amounts of potassium phenolate to the reacting system reduces the protic acidity and promotes ortho-regioselective tert-alkylation. These results are tentatively explained in terms of competition of ‘H-bond-template’ and ‘charge-controlled’ mechanisms.