5-Membered cyclic ethers via phenonium ion mediated cyclization through carbonate chemistry

Cyclization of 2-(2-hydroxyethyl)phenol via DMC chemistry in acidic conditions is herein discussed for the first time. Reaction conditions have been investigated and optimized. This substrate is quite appealing as it incorporates a 2-hydroxyethyl moiety in ortho to the aromatic hydroxyl group capable of stabilizing the related phenonium ion. When the reaction mechanism was investigated via theoretical calculations, the results suggest that the most favorable pathway encompasses a DMC-mediated formation of the phenonium ion that is converted into the 2-(2-methoxyethyl)phenol. The related cyclic ether is then formed via intramolecular cyclization of this intermediate. This peculiar cyclization reaction is another example of the versatility of DMC herein used as solvent, methoxycarbonylation agent and leaving group in the intramolecular cyclization leading to the phenonium ion.