Synthesis and spectroscopy of nine isomeric methylacephenanthrylenes

Article abstract of DOI:10.1002/recl.19931120105

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, (1)H NMR and UV-VIS spectroscopy.According to the (1)H 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.