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Biscyclohexane‐Annulated Diethyl Dipyrrindicarboxylates: Observation of a Dipyrrin Form with Absent Visible Absorption
Author(s) -
Tikhomirova Ksenia,
Anisimov Alexander,
Khoroshutin Andrey
Publication year - 2012
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201101729
Subject(s) - chemistry , absorption (acoustics) , pyrrole , absorption band , absorption spectroscopy , photochemistry , aryl , quantum chemical , proton nmr , crystallography , nitrogen , visible spectrum , stereochemistry , molecule , organic chemistry , physics , alkyl , optoelectronics , quantum mechanics , acoustics , optics
A series of 2,3;7,8‐biscyclohexano‐fused diethyl 5‐aryldipyrrin‐1,9‐dicarboxylates have been synthesized [aryl = phenyl, 3,4‐dimethoxyphenyl and 2,3,5,6,8,9,11,12‐octahydro‐1,4,7,10,13‐benzopentaoxacyclopentadecine‐15‐yl ( m ‐benzo‐15‐crown‐5)]. The obtained compounds were shown to exist in two equilibrium forms in solution, with one exhibiting a visible absorption band ( λ abs 468–485 nm), and the other, “vis‐silent” form, having no absorption band in the visible region. The “vis‐silent” form has been isolated and characterized by NMR analysis, including two‐dimensional techniques. Quantum chemical calculations have also been performed, yielding two main conformations with proximate and distant arrangements of the nitrogen atoms. In the latter conformation the pyrrole–pyrrolene fragments were found to be nearly orthogonal, with no long chain of conjugation. Computational results confirm the spectroscopic findings. Two different forms were also characterized as their Mg 2+ complex and investigated by UV/Vis and by NMR spectroscopic analyses and a clear difference was noted.