The synthesis of 13 trans-dimethyldihydropyrenes (bridged [ 14lannulenes) fused to one or more benzene, naphthalene, phenanthrene, phenalene, or quinoxaline rings and 6 cis-dihydropyrene derivatives from benzenoid precursors using either a thiacyclophane route or an electrocyclic addition of a furan to an annulyne followed by deoxygenation is reported. Their 'H NMR spectra are studied in detail to obtain correlations between 3 J~,~ coupling constants and the intemal methyl proton chemical shifts and also between the latter and the more distant external annulene ring proton shifts. These linear correlations are then used to obtain a relationship between the relative aromaticity of benzene and the fused ring in question, such that the aromaticity of the fused ring can be estimated relative to that of a benzene ring simply from a measurement of chemical shift in the fused annulene.

The aromatic ring current probe, the bridged [14]annulene dimethyldihydropyrene, 1, is used to investigate the bond localization effects of the organometallic species tricarbonylchromiumbenzene, 37, hexamethylbenzenerutheniumbenzene, 38, tricarbonylmanganesecyclopentadienyl, 40, and pentamethylcyclopentadienylrutheniumcyclopentadienyl, 39, when fused to the annulene. Benzo[a]dimethyldihydropyrene 2 was converted to the two isomers of its tricarbonylchromium complex, 9 and 10, in 60% yield using ligand exchange with naphthalene and to its hexamethylbenzene−ruthenium complexes 11 and 12 with [RuCl2(HMB)]2 and AgBF4. The cyclopentadienide fused dihydropyrene 5 was synthesized from dimethyldihydropyrene 1 in eight steps, and then on reaction with pentacarbonyl manganese bromide gave the tricarbonylmanganese complex of 5, as two isomers 28 and 29 in 61% yield, and with (Cp*RuCl2) n gave 70% yield of the dihydropyrene annelated ruthenocene isomers 26 and 27. Bis(tricarbonylchromium) complexes 32−34 were obtained in 50% yield from the dibenzannulene 30. The 1H NMR spectra for each complex were analyzed in detail with regard to ring current shielding of the internal methyl protons and ring current deshielding of the external protons. The McGlinchey equation was used to remove diamagnetic anisotropy effects, and the resultant chemical shift values were consistent with coupling constant results, which together yielded bond fixation data of the annulene, caused by the organometallic. The relative bond fixing ability of the organometallics was found to be in the order:  Cp−Ru−Cp* > benzene−Ru2+−(HMB) > Cp−Mn(CO)3 > benzene−Cr(CO)3 > benzene. Alternance parameter evidence is presented that the complexes are aromatic, and the authors discuss the relative aromaticity of the complexes to benzene.

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The reversible valence isomerization of cyclophanedienes to dihydropyrenes is discussed for a number of [a]- and [e]-annelated examples, 5 → 6 and 7 → 8, and is related to AM1 and MM2+Pi calculations. Only in [e]-fused systems is the isomerization easily seen to be reversible. Electrophilic substitution of dihydropyrenes is discussed. Nitration of the highly annelated 20 gives a mixture of 8- and 7-nitro derivatives, while NBS/DMF bromination of the benzo[a]dihydropyrene 3 gives mostly 12-bromo derivative.

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