p-Methoxybenzylation Reagent

4-Methoxybenzyl 2,2,2-Trichloroacetimidate (1) is a reagent for acid-catalyzed p-methoxybenzylation, and used as a protecting agent for an hydroxyl group. It reacts with an hydroxyl group in the presence of TfOH catalyst to produce p-methoxybenzyl ether.¹⁾ In this method, the reaction proceeds under mild conditions, and an hydroxyl group can be selectively protected without damaging acid- and alkali-sensitive groups. The p-methoxybenzyl (MPM) group is readily removed with DDQ in CH₂Cl₂-H₂O under neutral conditions.²⁾ It can be selectively removed since most of general protective groups such as the benzyl group are inactive under this condition. In addition, it is also possible to remove the benzyl group selectively while leaving the MPM group by catalytic reduction in the presence of Raney nickel catalyst. The application to the synthesis of compounds having complicated structures like natural products is expected by using these methods appropriately.