Synthesis of Stable Nonaromatic Fluorenonephyrin Macrocycle

Abstract A new derivative of our recently reported nonaromatic fluorenophyrin 5 named fluorenonephyrin 6 was synthesized over a sequence of six steps starting with commercially available fluorene as precursor. Our attempts to direct oxidation of 5 to 6 were not successful. Hence, we synthesized 2,7‐ bis (phenyl(1H‐pyrrol‐2‐yl)methyl)‐9‐fluorenone (fluorenone tripyrrane) in five simple steps from fluorene, and condensed it with pentafluorobenzaldehyde under mild acidic conditions in CH 2 Cl 2 followed by oxidation with DDQ and chromatographic purification to afford fluorenonephyrin (9%). 6 was characterized and studied by HR‐MS, 1D and 2D NMR spectroscopy, absorption, electrochemical and DFT/TD‐DFT techniques. The DFT studies revealed that 6 was more distorted than 5 and that introduction of C=O in the macrocyclic core remarkably distorts the pyrrole rings of the dipyrrin unit from the mean plane of macrocyclic framework. The macrocycle showed a band at around 390 nm and a broad band at around 650 nm. The redox properties indicated that the macrocycle was highly electron‐deficient in nature. TD‐DFT studies were in accordance with the experimental observations.