Abstract
In spite of unique structural, spectroscopic and redox properties, the synthetic variants of the planar, antiaromatic hexaphyrin (1.0.1.0.1.0) derivatives 2, has been limited due to the low yields and difficulty in access to the starting material. A chemical modification of the meso-substituents could be good alternative overcoming the synthetic barrier. Herein, we report a regio-selective nucleophilic aromatic substitution (SNAr) of meso-pentafluorophenyl group in rosarrin 2 with catechol. The reaction afforded benzodioxane fused rosarrin 3 as single product with high yield. The intrinsic antiaromatic character of the starting rosarrin 2 retained throughout the reactions. Clean, two electron reduction was achieved by treatment of 3 with SnCl2•2H2O affording 26π-electron aromatic rosarrin 4. The synthesized compounds exhibited noticeable changes in photophysical and redox properties compared with starting rosarrin 2.
Highlights
Upon vary ofshown naphthobipyrrole with1,pentafluorobenzaldehyde utilizing the reportedinprocerolidone (Scheme 1).tion in Scheme the reaction unexpectedly resulted the meso‐substituents from pentafluorophenyl group to bis(trifluoromethyl)phenyl gr 2 was treated with catechol in the presence of base (K2 CO3 ) One in Nexclusive formation dure of double nucleophilic aromatic substitution product methylpyrrolidone (Scheme 1)
Towar we report a synthesis of meso‐tris‐(1,2,4‐trifluorodibenzo(b,e)(1,4)dioxine tuted rosarrin (3) by a regio‐selective aromatic nucleophilic substitution reaction o rin (2)
The core-N-Hs of the rosarrin could be confirmed by found that applying SnCl2 dihydrate as a reducing agent resulted in efficient con appeared at −5.33 ppm as broad singlet which is in comparison with those observed for to the corresponding 26π electron aromatic form without any contamination of rosarrin 2
Summary
The flexible, non-planar structural property affects the overall aromaticity of the hexapyrrolic macrocycles as well as photophysical properties These hexapyrrolic macrocycles have been modified by many ways and has been explored in terms of coordination ability, changes in redox behavior, molecular orbital perturbations. The rosarrin 2, bearing pentafluorophenyl group at the meso-position, displayed reversible redox state changes from antiaromatic 24π electron system to aromatic 26π electron system upon protonation. Successful modifications at periphery and meso-substituents of the rosarrin enabled to isolate a 25π-electron species as air stable form [10]. This strategy was successfully impleplayed strong, intermolecular ‘face‐to‐face’, π‐π interaction between antiaromatic mole‐. Visaged to exploit this strategy to the modification of rosarrin to develop new rosarrins rins often encountered difficulties because varying meso‐substituents are synthetically and to explore their photophysical and redox chemistry.
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