Reactivity insights from the allylation of substituted phenols with 2-allyloxy-1-methylpyridinium triflate

Abstract

Allyl phenyl ethers are efficiently formed by generating 2-allyloxy-1-methylpyridinium triflate in situ followed by reaction with a phenol substrate under mildly basic conditions. Electron-poor phenols give excellent yields of the corresponding allyl phenyl ether, while electron-rich phenols typically give more complicated crude reactions mixtures, and ultimately lower yields of isolated ether product. Interestingly, one of the critical factors for a successful reaction is the shape and size of the reaction vessel, potentially due to maximizing the surface area of the insoluble molten oxypyridinium salt and the rest of the reaction mixture. The addition of dibenzo-18-crown-6 helps the efficiency of the reaction, presumably by slightly improving the solubility of the reaction components. These reaction conditions indicate that both the nucleophilic and electrophilic components of these reactions are important for an efficient reaction, even though the mechanism of substitution has typically been described as “SN1-like.”