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The synthesis of nine isomeric methyl-substituted acephenanthrylenes is described. Three different approaches were used. 1-, 2-, And 6-methylacephenanthrylene (1a, 1c and 1f) were prepared by formylation of acephenanthrene (2) and 4,5,7,8,9,10-hexahydroacephenanthrylene (17), followed by Wolff-Kishner reduction and dehydrogenation. 4-, 5-, 7- And 10-methylacephenanthrylene (1d, 1e, 1g and 1j) were synthesized by treating the corresponding acephenanthrenones with methyllithium, followed by dehydration and, in the case of 1g and 1j, dehydrogenation. 8- And 9-methylacephenanthrylene (1h and 1i) were prepared by a Haworth synthesis starting with the reaction of methylsuccinic anhydride with acenaphthene. The spectroscopic properties of acephenanthrylene and its methyl derivatives were investigated with mass spectrometry, 1H NMR and UV-VIS spectroscopy. According to the 1H NMR spectra, steric hindrance between the methyl group and nearby protons decreases in the following order: 1, 10 > 6 > 7 > 3 > 4, 5, 8, 9. |
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