Partially protected form of 2-imidazolidinone, used by Meth-Cohn's group to react with 2,6-Difluoropyridine, A15522, in the synthesis of linear and macrocyclic ligands with alternating pyridine and 2-imidazolidinone units. The t-butyl group can be readily removed in dilute acid: J. Chem. Soc., Perkin 1, 423 (1998).