Simple methodology for syntheses of porphyrins possessing multiple peripheral substituents with an element of symmetry

New methodology was developed for synthesis of regiochemically pure porphyrins with D-2h symmetry (e.g. 9) via tetramerization reactions involving two different pyrroles. The two pyrrole components were a 2,5-diunsubstituted pyrrole (e.g. 11) and a 2,5-bis[(N,N-dimethylamino)methyl]pyrrole (e.g, 10), the latter being formed from a 2,5-di-unsubstituted pyrrole by treatment with excess Eschenmoser's reagent (N,N-dimethylmethyleneammonium iodide). A bis-butanoporphyrin 16 was transformed into the corresponding opp-bis-benzoporphyrin 17 by treatment with DDQ. The synthetic method was further extended to allow the synthesis of more unsymmetrical porphyrins, with C-2v symmetry (e.g. 32), by reacting a tripyrrane (e.g. 27) with a 2,5-bis[(N,N-dimethylamino)methyl]pyrrole (e.g. 18). The structures and substituent arrays in both type of porphyrins were confirmed by single-crystal X-ray crystallography.