Geometrical Analogues of Purine Substrates (5-Methyladenine, Pyrolysis, Diazabiphenylene)

85 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.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.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD