Supramolecular cavitands that contain inwardly directed functional groups have yielded specialized transformations and trapping of reactive intermediates. A recently reported 3‐wall Au cavitand provides exciting opportunities for supramolecular catalysis. In this study, a variety of substituted γ‐alkynoic acids were reacted to give lactones. The interaction of peripheral “R” groups revealed differential catalyst behavior. Extremely large and small groups reacted with appreciable rate. Intermediate sized groups however, slowed significantly: giving support that size‐specific binding is at play when using cavitands as a scaffold for gold catalysis. These results serve as some of the first evidence of the interplay between substrate and cavitand interior in the catalytic sphere.