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Title:Synthesis Of 1,10- And 3,8-alkyl Substituted Pyrido(1",2": 1',2')imidazo(4',5': 4,5)imidazo(1,2-(italic-a))pyridines
Author(s):Clauson, Gary Lewis
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Organic
Abstract:The 1,10-dimethyl-, 1,10-bis(isopropyl)-, and 3,8-dimethyl-substituted pyroid 1'',2'':1',2' imidazo 4',5':4,5 imidazo 1,2-a - pyridines have been synthesized and their properties compared with those of the parent compound.
The precursors to these dipyridotetraazapentalenes, N-(2-pyridinyl)imidazo 1,2-a pyridines, were synthesized by the reaction of chloroketene diethyl acetal with the appropriate 4- or 6-alkyl- pyridin-2-amine in acetic acid/pyridine, which was prepared by alkylation of the 6-alkyl-2-(2,5-dimethyl-1-pyrrolyl)pyridine or by the Tschitschibabin reaction on the 4-alkylpyridine.
The tetraazapentalenes were prepared from the precursors by oxidation with iodobenzene diacetate. The difficulty in obtaining the bis-tert-butyl compound can be attributed to maximal steric hindrance in the formation of the final bond.
The fluorescence of the compounds in the 1,10-disubstituted series varies with increasing size of substituent; the emission wavelength increases and the quantum yield decreases in going from H to isopropyl.
Although MM2 molecular mechanics calculations predicted helicity (and, thereby, chirality) for the 1,10-dialkyl compounds, they were found to exist as helical enantiomers only in the solid state, as shown by X-ray crystallography. A variable temperature ('1)H NMR study on the bis(isopropyl) compound showed that the methyl groups were interconverting rapidly at room temperature in solution, thus making the molecules achiral in solution. Isolation of the enantiomers therefore seems unlikely.
Complete NMR spectral assignments on all compounds prepared were accomplished through various methods, including short and long range heteronuclear.
Comparison of the angles, bond lengths, and Van der Waals distances of the parent, 1,10-dimethyl, and 1,10-bis(isopropyl) compounds reveals that there are only slight changes in the central 5/5 system and a twisting of the outer pyrido rings to accommodate the larger substituents. The minor variations between the dimethyl and bis(isopropyl) compounds suggests that the ring system is strained to the limit even with methyl substituents. The MM2-calculated and X-ray structures are remarkably similar in all aspects, showing the power of molecular mechanics calculations for these compounds.
Issue Date:1987
Description:146 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
Other Identifier(s):(UMI)AAI8711784
Date Available in IDEALS:2014-12-15
Date Deposited:1987

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