2,4-Ethoxycarbonyl-7,12-methano-3
H-cyclohepta[10]annulene-3-one (1) was synthesized starting from 3,4-bis(bromomethyl)-1,6-methano[10]annulene by a two step process. Then, the treatment of (1) with NaOH / MeOH and followed by heating in DMF at 100 °C gave parent 7,12-methano-3
H-cyclohepta[10]annulene-3-one (2). The
1H-NMR spectra of bridged annulene moiety of (1) and (2) are observed at lower field than that of 1,6-methano[10]annulene. And the
1H-NMR spectra of (1) and (2) in strong acidic media indicates the formation of cationic species by protonation and the
1H-chemical shifts of bridged methylene showed the greater contribution of homoconjugation in bridged annulene moiety. The shorter distance between C7 and C12 compared to that of parent [10]annulene shown by X-ray crystallography also support the contribution of homoconjugation.
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