Syntheses and properties of trimethyltetradehydroannulenones and the benzannelated derivatives
Syntheses of 5,10,15-(8) and 2,5,10-trimethyl-6,7,8,9-tetradehydrocyclopentadecenone (12), and 8,13-(9) and 6,13-dimethyl-14,15,16,17-tetradehydrobenzocyclopentadecen-7-one (13), 8,13-(10) and 10,13-dimethyl-14,15,16,17-tetradehydrobenzocyclopentadecen-9-one (14), and 8-methyl-(11) and 6-methyl-16,17,18,19-tetradehydrodibenzo[a,g]cyclopentadecen-7-one (15) are described. The influence of α-methyl substitution and benzannelation upon the structure and tropicity of the tetradehydroannulenone ring system is discussed in view of the 1H n.m.r. and u.v. spectra of these annulenones, as well as those of the α-methyl unsubstituted annulenones (4)–(7).