Novel cyclobutene-fused aromatic systems

Date
1983
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Abstract

The insertion of methylene into the aromatic ring of benzocyclobutene leads to a mixture of cyclobutene-fused cyclOheptatrienes. Treatment of this mixture with a trityl salt affords the cyclobutene-fused tropylium salt in essentially pure form. If this same synthetic approach is applied to other annelated benzenes, bis- and tris-annelated salts can be prepared. The proton and carbon-13 nmr spectra of a series of annelated tropylium salts have been analyzed and interpreted in terms of a rehybridization theory. With decreasing size of the annelated rings the chemical shift of the carbon ortho to the bridgehead moves upfield and the chemical shift of the bridgehead carbons moves downfield. The aromatic proton chemical shift of the annelated tropylium salts shows anomalous behavior but the aromatic C-H coupling constant increases with the decreasing size of the annelated rings. A shift to longer wavelength absorption in the UV is observed upon increasing annelation. The molar absorptivity (extinction coefficient) is found to increase as the size of the fused rings is decreased. [...]

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Keywords
Benzene, Aromatic compounds, Alicyclic compounds
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