Diazoacetate esters proved to be suitable neutral guests for the self-assembled resorcin[4]arene hexameric capsule. The hydrogen- bonded supramolecular host catalyzed the 1,3-dipolar cycloaddition reaction between diazoacetate esters and electron- poor alkenes such as acrolein, acrylonitrile, crotonaldehyde, trans-2-hexenal, methyl, and butyl acrylate, which led to the corresponding 4,5-dihydro-1H-pyrazole derivatives. The cycloaddition reaction occurred within the cavity of the capsule. In fact, substantial inhibition of the catalytic activity was observed by employing tetraethylammonium tetrafluoroborate characterized by greater affinity for the hexameric capsule as a competitive guest; its presence inhibited access of the substrates. The 1,3-dipolar cycloaddition reaction between diazoacetate esters and acrylate esters of different lengths showed a significant degree of substrate selectivity owing to the encapsulation of the reagents before the cycloaddition reaction.