Highly selective non-catalytic Claisen rearrangement in a high-pressure and high-temperature water microreaction system

High-pressure and high-temperature water (HPHT-H2O) microreaction system was proven to be an efficient method to carry out the non-catalytic Claisen rearrangement. Allyl phenyl ether undergoes Claisen rearrangement to obtain o-allylphenol with a very high yield and selectivity of 98% within a short reaction time of 13.4 s at 265 °C and 5 MPa pressure. Compare to the solvent-free microreaction, HPHT-H2O plays an important role to accelerate the reaction as a catalyst by transferring a proton along locally formed hydrogen bond with the substrate. Finally, the obtained product can be separated completely from the aqueous suspension within the time range of 40 min to 24 h after the reaction. Even though the reaction has occurred in aqueous conditions, little side reactions, such as hydrolysis, hydration, or pyrolysis, was found.