First Synthesis of Dodecasubstituted Porphycenes

The synthesis of dodecasubstituted porphycenes has not been reported, to date. Herein, the preparation of tetramethyloctaethylporphycene by a McMurry‐type coupling of 3,3′,4,4′‐tetraethyl‐5,5′‐diformyl‐2,2′‐bipyrrole was attempted at first, but dodecasubstituted porphycene was not successfully obtained and only pyrrolocyclophene was obtained. The structure of the pyrrolocyclophene was determined by 1H NMR spectroscopy, FAB MS, and X‐ray crystal‐structure analysis. The pyrrolocyclophene was not successfully oxidized to porphycene. Then, the McMurry‐type coupling of bicyclo[2.2.2]octadiene (BCOD)‐fused 5,5′‐diacyl‐2,2′‐bipyrroles was performed and tetra‐meso‐octa‐β‐substituted (dodecasubstituted) porphycenes were successfully obtained for the first time. The structures were determined by 1H NMR spectroscopy and X‐ray crystal‐structure analysis. The crystal structures and NMR spectra were compared carefully with octasubstituted porphycenes, and there was a good correlation between the position of the substituents, the N1N2 and N1N4 distances of the porphycene inner nitrogen atoms, and NMR chemical shifts of the inner NH protons, which expressed the strength of NH⋅⋅⋅N hydrogen bonding between N1 and N2. These results suggested that the BCOD structure was relatively compact compared with common alkyl groups and that was why the dodecasubstituted porphycenes were available this time. UV/Vis absorption and fluorescence properties are also discussed. Square versus rectangle: Dodecasubstituted porphycenes were prepared, for the first time, by taking advantage of the unique features of bicyclo[2.2.2]octadiene‐fused 2,2′‐dipyrroles. The retro‐Diels–Alder reaction of dodecasubstituted porphycenes gave meso‐substituted tetrabenzoporphycenes (see figure).