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Competitive formation of helical cycloocta- and cyclododecapyrroles
J A Wytko1, M Michels, L Zander
1Laboratoire d'Electrochimie et de Chimie Physique du Corps Solide, Université Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg, France.
The Journal of Organic Chemistry
|January 11, 2000
Summary
Researchers aimed to synthesize gem-dimethyl-substituted cyclotetrapyrroles but instead formed larger macrocycles, cyclooctapyrrole and cyclododecapyrrole. These novel compounds exhibit dynamic behavior in solution and were structurally characterized.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Macrocyclic Chemistry
Background:
- Exploration of electronic effects in spiro-dicorrole and its Ni(II) complex.
- Interest in gem-dimethyl-substituted cyclotetrapyrrole and its Ni(II) complex.
- Previous studies on polypyrrole macrocycles and their complexes.
Purpose of the Study:
- To synthesize gem-dimethyl-substituted cyclotetrapyrrole (2a) and its Ni(II) complex (2b).
- To investigate the products of acid-catalyzed condensation reactions involving specific pyrrole precursors.
- To characterize newly formed macrocycles and study their structural and dynamic properties.
Main Methods:
- Acid-catalyzed (1 + 1) condensation of dimethyldipyrrylmethane (3) and diformylbipyrrole (4).
- Isolation and purification of condensation products, including cyclooctapyrrole (6) and cyclododecapyrrole (7).
- Structural characterization using variable temperature 1D and 2D NMR spectroscopy and single-crystal X-ray diffraction.
- Analysis of dynamic behavior in solution through NMR spectroscopy.
Main Results:
- The desired gem-dimethyl cyclotetrapyrrole was not formed.
- Unexpected (2 + 2) and (3 + 3) condensation products, cyclooctapyrrole (6) and cyclododecapyrrole (7), were obtained.
- Cyclododecapyrrole (7) was the major product and is one of the largest known cyclopolypyrroles.
- Both macrocycles (6 and 7) exhibit dynamic conformational behavior in solution.
- Solid-state structures determined by X-ray diffraction closely matched low-temperature solution conformers.
Conclusions:
- Acid-catalyzed condensation of specific pyrrole precursors leads to larger macrocycles rather than the intended cyclotetrapyrrole.
- The synthesized cyclooctapyrrole and cyclododecapyrrole are novel macrocycles with significant size.
- These macrocycles display complex dynamic behavior in solution, with distinct conformations at different temperatures.
- Structural data from solid-state and solution studies provide insights into macrocycle conformation and dynamics.