The impact of Novel Process Windows on the Claisen rearrangement

The impact of Novel Process Windows on the Claisen rearrangement in microflow was investigated. Elevated temperatures (up to 300 °C) were crucial to achieve full conversion of allyl phenyl ether in the Claisen rearrangement. We observed that 1-butanol was the optimal reaction solvent for this transformation in flow. Solvent-free reaction conditions were feasible for the Claisen rearrangement and provided quantitative yields of the target product at 280 °C and 100 bar. Also elevated reaction pressures (up to 300 bar) were investigated in the Claisen rearrangement. We found that thermal expansion and pressure-related compression phenomena cannot be ignored at such harsh reaction conditions. These phenomena lead to large deviations of the desired residence time (as calculated from the nominal flow rate) and have a clear impact on the observed reaction trends. Finally, we also investigated the temperature effect on the Johnson–Claisen rearrangement of cinnamyl alcohol. Quantitative yields were obtained at 200 °C and at 100 bar.