Synthesis and structures of ethoxymethylene derivatives of 1,3-diethoxycyclohexenylium perchlorate

1,3-Diethoxy-4,6-di(ethoxymethylene)-5,5-dimethylcyclohexenylium perchlorat e (6a) was synthesized from 1,3-diethoxy-5,5-dimethylcyclohexenylium perchl orate by successive introduction of ethoxymethylene groups. Perchlorate 6a was also obtained from dimedone in one preparative step. Compound 6a was st udied by X-ray diffraction analysis. The bond lengths in the fragment conta ining the C(1)-C(4) and C(6) atoms of the six-membered ring of the cation a re substantially equalized and close to the C-arom-C-arom bond length. Appa rently, this fact indicates that the positive charge is primarily delocaliz ed over the aromatic system.