A NOVEL SYNTHETIC ROUTE TO SAPPHYRINS

New methodology has been developed for the synthesis of so-called sapp hyrins, pentapyrrolic ''expanded porphyrins''. An efficient approach i nvolving acid-catalyzed condensation of 1,19-diunsubstituted a,c-bilad ienes and 3,4-dialkylpyrrole-2-carbaldehydes eliminates the preparatio n of bipyrrolic intermediates and allows the synthesis of sapphyrins w ith an unsymmetrical array of peripheral substituents. The beta-substi tution pattern of ,17-tetraethyl-7,8,12,18,22,23-hexamethylsapphyrin h as been unambiguously confirmed by single crystal X-ray crystallograph y. H-1 NMR spectra of the dication salts of sapphyrins are strongly de pendent upon the counterions, and the pattern of resonances observed i n solution is related to the stacking interactions between the macrocy cles.