Novel phosphonated bicyclic frameworks from Diels–Alder reaction as chelating agents of di- and trivalent metal cations

The synthesis of novel [4+2] cycloadducts by Diels–Alder (DA) reaction between diethyl 1-phosphono-1,3-butadiene and cyclic CC and NN dienophiles, such as maleimide and 1,2,4-triazole-3,5-dione derivatives, is described. These phosphonated bicyclic frameworks feature a cage shape enabling metal chelation. Indeed, stable complexes were formed in solution with M2+ and M3+ metal cations, as evidenced by HRMS in the ESI mode (electrospray ionization). L1:M (one ligand–one metal) and L2:M (two ligands–one metal) complexes were identified depending on the nature of the cation.