Effect of 1,4-naphthoquinone annelation on the conformational behavnniour of carbonyl- and methano-bridged cyclodecadiene derivatives

The Na2Cr2O7 oxidation of hexahydro-7,16-methanodinaphtho[2,3-a:2′,3′-f] cyclodecene derivative 2, produced two bis-(1,4-naphthoquinone)s, 7 and 9, and monoquinone compound 8. Benzonaphtho derivative 3 gave two 1,4-naphthoquinone derivatives, 10 and 11, on oxidation.Flexible compounds 7–11 showed temperature-dependent 1H NMR spectra due to equilibria among chair–boat, twin-chair, and boat–chair conformers, which were 1H NMR spectroscopically, characterized. A twin-chair conformer was detected in products 8, 9 and 10, but not in compounds 7 and 11. A broad absorption band due to an intramolecular C–T interaction in the twin-chair conformer was observed at λ∼ 400 nm in the electronic spectra of the monoquinones, 8 and 10, but not in the bis(quinone)9. Population of the twin-chair conformer increased with removal of the ester group on the bridgehead position. Reduction of the carbonyl group on the bridge also favoured the twin-chair conformation, indicating a repulsive interaction between the ester and the carbonyl group of the 1,4-naphthoquinone moiety. Upon irradiation with sunlight, compound 7 gave the [2 + 2]-photoadduct 15.