Structure–performance landscape of N-alkoxyphthalimides as organocatalysts in aerobic oxidation

Abstract N -Alkoxyphthalimides were studied to design new-type organocatalysts for aerobic oxidation that are capable of metal/initiator-freely forming both phthalimide N -oxyl radicals and alkyl radicals in situ via their light/heat-induced homolysis. Our results show that their >NO–C bond strengths and HOMO-LUMO gaps change greatly upon altering N -alkoxy groups, which greatly decrease when their N -alkoxy groups include steric fluorenyl, xanthenyloxy, or triphenylmethyl groups. The conventional substituents on the bilateral phenyl rings of N -benzyloxyphthalimide have negligible effects on their >NO–C bond strengths, but significantly tune their HOMO-LUMO gaps. The photochemical activity of N -benzyloxy-4-aminophthalimide and N -4-amino-benzyloxyphthalimide may be similar to that of known N -triphenylmethyloxyphthalimide and N -diphenylmethyloxyphthalimide. Both the thermal and photochemical stability of N -acetyloxyphthalimides are higher than those of N -alkoxyphthalimides, but their hydrolysis to form N -hydroxyphthalimide is more favorable. The present work allows a reasonable prediction of the catalytic performance of N -alkoxyphthalimides and provides a new perspective for the rational design of organocatalysts for industrial applications.