Ruthenium-catalyzed intermolecular alkene–alkyne couplings in biologically relevant media

Cationic cyclopentadienyl Ru(ii) catalysts can efficiently promote mild intermolecular alkyne–alkene couplings in aqueous media, even in the presence of different biomolecular components, and in complex media like DMEM. The method can also be used for the derivatization of amino acids and peptides, therefore proposing a new way to label biomolecules with external tags. This C–C bond-forming reaction, based on simple alkene and alkyne reactants, can now be added to the toolbox of bioorthogonal reactions promoted by transition metal catalysts.