The present disclosure features a strain-promoted [2+2+2] reaction that can be carried out under physiological conditions. In general, the reaction involves reacting a pi-electrophile with a low lying LUMO with a quadricyclane on a biomolecule, generating a covalently modified biomolecule. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo and in vitro. The reaction is compatible with modification of living cells. In certain embodiments, the pi-electrophile can comprise a molecule of interest that is desired for delivery to a quadricyclane-containing biomolecule via [2+2+2] reaction.