Efficient preparation and processing of the 4-methoxybenzyl (PMB) group for phenolic protection using ultrasound.

Power ultrasound efficiently facilitates the rapid preparation and reaction of 4-methoxybenzyl chloride (PMB-Cl) 1 in providing protected phenolic ether intermediates for organic synthesis. Using two-phase systems in both the ultrasound-promoted preparation and reactions of PMB-Cl, typical runs produce PMB-protected products within 15 min. When compared with nonsonicated control reactions, the results demonstrate clear advantage in terms of efficiency when the protocol is applied to the mild and selective protection of various multisubstituted phenols including sensitive phenolic aldehydes.