Synthesis of new bis(2-[1,8]naphthyridinyl) bridging ligands with multidentate binding sites

A series of new 2-[1,8]naphthyridinyl and bis(2-[1,8]naphthyridinyl) bridging ligands with multidentate binding sites were prepared using 2-amino-5-cyano-6-ethoxy-4-phenyl-3-carbaldehyde pyridine as excellent Friedländer synthon. Condensation with a series of acetyl(heteroaryl)aromatics provides the corresponding 2-aryl(heteroaryl)-1,8-naphthyridines. Reaction with 1,3-diacetylbenzene, 2,6-diacetylpyridine or 4-tert-butyl-2,6-diacetylpyridine provides the expected Friedländer product. Similar 2:1 condensation with 1,4-diacetylbenzene, 4,4′-diacetylbiphenyl, 1,4- and 1,6-diacetylpyrene, 2,6-diacetylpyrazine or 2,3-butanedione leads to a family of six new bis-1,8-nap ligands. The reaction with cyclic 1,2- or 1,3-diketones affords 3,3′-annelated derivatives of all-syn or all-trans planar 2,2′-nap, respectively. Examination of the electronic absorption and emission spectra of the bridging ligands was realized.