Zooming in on the hydrated imidazoline ring expansion: Factors influencing the rate of N → N' aroyl migration in N-aroyl-N-(hetero)aryl ethylenediamines

The influence of electronic factors on the rates of N -> N' aroyl migration in N-aroyl-N-(hetero)aryl ethylenediamines has been examined. Electron-withdrawing substituents on the aroyl group were found to weakly accelerate the reaction (in linear correlation with the Hammett sigma(p) constants). Much stronger influence came from the nitrogen-bound aromatic group which gave a strong linear correlation with the Hammett sigma(p) constants. For electron-deficient heteroaromatics and nitroaromatics, the migration was nearly instantaneous in basic medium. These findings will significantly impact the planning of mechanistically related transformations of N-(2-aminoethyl) lactams through the hydrated imidazoline ring expansion (HIRE) process. (C) 2020 Elsevier Ltd. All rights reserved.