Initial syntheses of 17 were run at molar ratios of 1:1, 2:1 and 3:1 of isothiocyanate starting material to 3-NH2-β-CD, keeping all other reaction conditions constant. The reaction proceeded successfully only when the isothiocyanate reactant was present at 3:1 excess and gave yields <35%. We hypothesized that the isothiocyanate was acting as a guest molecule, binding inside the β-CD cavity and hindering progress of the reaction. To explore this hypothesis, we added a competing guest molecule, adamantane, to block the β-CD cavity. Adamantane is an inert hydrocarbon, known to have a strong affinity for β-CD . This approach was successful, as a reaction mixture 1:1:1 of adamantane, 3-NH2-β-CD and isothiocyanate yielded 17 at 83% yield. The adamantane was easily removed during the acetone wash purification stage of the workup. Thioureas 18-19 and an analogous urea Compound, 20, were also successfully synthesized at high yield (Figure ) by this procedure.