- Porphyrins with exocyclic rings. Part 24. Synthesis and spectroscopic properties of pyrenoporphyrins, potential building blocks for porphyrin molecular wires
-
Porphyrins with fused pyrene units have been prepared by '2+2' and '3+1' methodologies. Nitration of 1,2,3,6,7,8-tetrahydropyrene, followed by oxidation with DDQ, gave 4-nitropyrene and this condensed with ethyl isocyanoacetate in the presence of DBU or a phosphazene base to generate a pyrenopyrrole ethyl ester. Ester saponification and decarboxylation with KOH in ethylene glycol at 190 °C gave the parent pyreno[4,5-c]pyrrole and this was further condensed with 2 equiv of acetoxymethylpyrroles to afford the corresponding tripyrranes protected at the terminal positions with tert-butyl esters. In a one pot procedure, the ester protective groups were cleaved with TFA and following dilution with dichloromethane, '3+1' condensation with a pyrrole dialdehyde, and dehydrogenation with DDQ, the targeted pyrenoporphyrins were generated in good overall yields. A dialdehyde was also prepared from the pyrenopyrrole intermediate and this reacted to give an opp-dipyrenoporphyrin. The pyrenopyrrole ethyl ester reacted with dimethoxymethane in the presence of an acid catalyst to give a dipyrenopyrrolylmethane, and this was used to prepare an adj-dipyrenoporphyrin using the MacDonald '2+2' approach. The pyrenopyrrole dialdehyde was also used to prepare a porphyrin with fused pyrene and phenanthroline moieties. Although the UV-vis spectra of these new porphyrin systems are unexceptional, pyrenoporphyrins show many of the features necessary for the construction of porphyrin molecular wires.
- Gandhi, Virajkumar,Thompson, Michelle L.,Lash, Timothy D.
-
experimental part
p. 1787 - 1799
(2010/04/06)
-
- Spectroscopic and photochemical properties of mononitropyrenes
-
The influence of the nitro group on the aromatic ?-system of pyrene has been studied by comparing the spectroscopic and photochemical properties of the three mononitropyrenes.Whereas the UV and mass spectra of 1- and 4-nitropyrene show an interaction normal for nitro-aromatic compounds, this is not observed for 2-nitropyrene.The lack of interaction is reflected in a UV spectrum very similar to that of pyrene and a mass spectrum with a very low abundance of M-NO.The photochemical behaviour of the three compounds is governed by the degree of interaction. 1-Nitropyrene shows the nitro-nitrite rearrangement leading to 1-hydroxypyrene (88percent) and 1-hydroxy-2-nitropyrene (7percent).The photoproducts of 4-nitropyrene are pyrene (9percent) and unstable products which react with the solvent. 2-Nitropyrene is very stable under photochemical conditions due to lack of interaction.Similarly, the sterically hindered 1-methyl-2-nitropyrene is also very stable towards light.The photochemical nitro-nitrite rearrangement observed for nitro-aromatic compounds was found to be governed by electronic effects.
- Braken-van Leersum, A. M. van den,Tintel, C.,Zelfde, M. van't,Cornelisse, J.,Lugtenburg, J.
-
p. 120 - 128
(2007/10/02)
-