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8096832 
Journal Article 
Toward the Understanding of Benzannelated Annulenes: Synthesis and Properties of [a]-Ring Monobenzannelated Dihydropyrenes 
Mitchell, RH; Carruthers, RJ; Mazuch, L; Dingle, TW 
1982 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
104 
9 
2544-2551 
English 
The benzannelated dihydropyrenes 3 and 4 were synthesized from 1,3-bis(bromomethyl)naphthalene (16) and 1,3-bis(bromomethyl)-2-methylnaphthalene (22) (the latter obtained in 18% yield in seven steps from 2,3-dimethylnaphthalene) in 7.4% and 4.8% overall yields, respectively, using Stevens or Wittig rearrangement-Hofmann elimination sequences on the dithiacyclophanes 13 and 14, followed by valence tautomerization of the resulting cyclophanedienes 11 and 12. The dihydrobenzopyrene 3 rapidly dehydrogenates to benzo[a]pyrene (21), whereas the dimethyl derivative 4 is relatively stable. The internal protons of 3 and 4 show only about 50% of the shielding of the corresponding protons in the parent hydrocarbons 8 and 1, respectively, and this effect is ascribed to bond localization caused by the benzannelating ring. The residual diatropicity of 3 or 4 is larger than that for the related less rigid 40 or 41. Unlike the parent 1, no evidence was found for a reversible valence isomerization of 4 to 12. Coupling constants of the external protons of 4 were used to compare bond orders to calculated ones, and it was shown that both rings of 4 considerably perturb the derealization of the other, in accordance with Günther's calculations. A comparison of the 1H NMR spectra of 4 and benzo[a]pyrene (21) was made. © 1982, American Chemical Society. All rights reserved.