A Calorimetric Investigation To Safely Scale-Up a Curtius Rearrangement of Acryloyl Azide

N-Vinyl-O-benzyl urethane was prepared for use as a starting material in a multistep synthesis of a drug candidate. After unsuccessful attempts to employ non-Curtius options to prepare this intermediate, we decided to assess the thermodynamic and kinetic parameters of the acyl azide Curtius rearrangement and trapping of the intermediate isocyanate. (Prepared in analogy to the literature method of Hegedus et al.: Wieber, G. M.; Hegedus, L. S.; Akermark, B.; Michalson, E. T. J. Org. Chem. 1989, 54, 4649−4653.) Reaction calorimetry was utilized to show that the rate of the Curtius rearrangement was completely dose-rate controlled, and that under carefully defined conditions this reaction could be safely performed on limited scale. In addition to addressing the thermal hazard issues, profiling the reaction with reaction calorimetry and interfaced technologies resulted in significant process improvements.