Synthesis of elongated cavitands via click reactions and their use as chemosensors

A very efficient modular reaction protocol was developed to attach various functionalities to a rigid cavitand scaffold. In this way, aryl, iodoaryl, benzyl, pyrrolidylmethyl groups, as well as a polyethylene-glycol chain were attached to the ‘triazol-level’ of the cavitand. The palladium-catalyzed ethynylation of the iodoarene moieties, followed by the copper(I)-catalyzed azide–alkyne cycloaddition produced novel cavitands with significantly elongated binding pockets. The dimensions of these molecules are calculated to be at least 9 Å×18 Å, which place them amongst the largest unimolecular hosts obtained by pure covalent synthesis. A cavitand-based click conjugate is used for selective complexation of Cu2+ and Fe3+, providing significant fluorescent quenching.