AgOTf-promoted transetherification of p-methoxybenzyl ethers with allyl and benzyl bromides

Abstract

Conventional transetherification involves activation of the ether C–O bond, enabling either C–O/O–H bond metathesis with alcohols or C–O/C–O metathesis with other ethers. Here, we report an alternative approach based on an unusual C–O/C–Br bond metathesis. Silver triflate (AgOTf) promotes the transetherification of p-methoxybenzyl ethers (PMB–OR²) with allyl or benzyl bromides (R¹–Br), selectively affording unsymmetrical ethers (R¹–O–R²). The reaction tolerates a wide range of functional groups that are incompatible with the strong bases required for Williamson ether synthesis. Furthermore, the method enables a three-component process involving R¹–Br, R²–Br, and PMBOH, where PMBOH acts as an “oxygen linker” through a sequential etherification/transetherification process. Mechanistic studies indicate a cationic pathway proceeding via a trialkyl oxonium intermediate.