Geometrical Analogues of Purine Substrates (5-Methyladenine, Pyrolysis, Diazabiphenylene)
Bakthavachalam, Venkatesalu
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https://hdl.handle.net/2142/70230
Description
Title
Geometrical Analogues of Purine Substrates (5-Methyladenine, Pyrolysis, Diazabiphenylene)
Author(s)
Bakthavachalam, Venkatesalu
Issue Date
1984
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Abstract
Synthetic approaches are developed to cyclobutadienopurines and lin-benzocyclobutadienopurines, new extended purine analogues, by means of flash vacuum pyrolysis of suitable condensed pyridazine precursors. As a model for the cyclobutadienopurine ring system, benzo{3,4}cyclobutadieno{1,2-d}imidazole was prepared by thermal extrusion of dinitrogen. As expected of biphenylene analogues with increased electron density in the four-membered ring, the benzocyclobutadienoimidazole underwent extensive decomposition.
The first examples of the 1,3-diazabiphenylene ring system were synthesized by pyrolysis of pyrimidocinnoline precursors as preludes to the synthesis of lin-bcb-purines. A peculiar transformation of the 1,3-diazabiphenylene ring system into the isoquinoline ring system was observed when 4-chloro-1,3-diazabiphenylene was treated with sodium methoxide in methanol. The intermediacy of a benzodiazocine between two electrocyclic reactions was proposed for this transformation.
Several pyrimido{5,6-i}imidazo{4,5-g}cinnolines were prepared to serve as precursors for the synthesis of lin-bcb-purines in pyrolysis reactions. Chloro, methoxy, or trimethylsilyloxy precursors with N-benzyl and N-trimethylsilyl protecting groups failed to produce lin-bcb-purines on attempted pyrolysis. The unsubstituted precursor, pyrimido{5,6-i}imidazo{4,5-g}cinnoline, however, provided imidazo{4,5-h}-1,3-diazabiphenylene, the new purine analogue lin-bcb-purine.
Semiempirical molecular orbital calculations based on a MINDO/3 program were performed on 5-methyl-5H-adenine and its proposed intermediacy in a translocative rearrangement. The results revealed the relative instability of 5-methyladenine with respect to the stability of the final rearrangement product 4-amino-8-methylimidazo{1,5-a}triazine. The calculations also provided insight into the probable loci of bond-breaking and into the structures of the potential intermediates in the ring opening of 5-methyladenine.
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