The effect of the solvent
and the counter-ion on the ring alkylation of 3- and 4-methoxyphenols by
isopentenyl bromide has been examined. Under strictly anhydrous conditions good
and consistent yields of the o- isopentenylphenols were obtained with the combination
potassium- toluene, but sodium-toluene was more convenient. ��� Boron trifluoride etherate was more
satisfactory than stannic chloride, zinc chloride, or phosphoric acid in
catalysing the condensation of 3- and 4-methoxy-phenols with 2-methylbut-3-en-2-ol
to the corresponding o-isopentenylphenols. Aryl α,α-dimethylpropargyl
ethers were partially hydrogenated to the corresponding α,α- dimethylallyl
ethers which rearranged in boiling N,N-diethyl-aniline to o-isopentenylphenols
in high overall yield.