The insertion of methylene into the aromatic ring of benzocyclobutene leads to a mixture of cyclobutane-fused cycloheptatrienes. Treatment of this mixture with a trityl salt affords the cyclobutane-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 ...
