The Thermal ortho-Substitution of Phenols by Vinyl Ethers

Abstract

Pyrolysis of a mixture of phenol and 3,4-dihydro-2H-pyran (6) at 150- 180°C resulted in the formation of 2-(tetrahydro-2H-pyran-2-yl)phenol (3a) in moderate yield. This selective ortho-substitution reaction has been investigated for a range of phenols and a number of vinyl ethers. While it was found to be a fairly general reaction for phenols, only with the vinyl ether (6) and 2,3-dihydrofuran (28a) was the reaction found to be regioselective. Aluminium phenylate strongly catalyses the reaction of phenol with (6), which proceeded under these conditions at room temperature. An ene -type mechanism is proposed for the reaction.