The condensation of a Kemp's triacid derivative with a diamino resorcinarene yielded a cavitand with the deepest cavity prepared to date featuring an inwardly-directed carboxylic acid. The extended 6,7-diaminoquinoxaline wall bearing the acid allowed accommodation of large amines, such as 1-adamantanemethylamine, as well as smaller amines such as triethylamine. Adamantyl and cyclohexyl isocyanides are also bound in the deep cavitand in a way that positions the isonitrile function near the carboxylic acid group. Reaction occurs inside the cavity at ambient temperature to form the respective N-acylformamides. Low concentrations of the transient O-acyl isoamide intermediate were detected by (1)H NMR and IR spectroscopy.