Syntheses and properties of methyl-substituted benzannelated tetradehydro[13]annulenones

Abstract

Syntheses of 6,11-dimethyl-(6) and 8,11-dimethyl-12,13,14,15-tetradehydrobenzocyclotridecen-7-one (7) and 6-methyl-14,15,16,17-tetradehydrodibenzo[a,g]cyclotridecen-7-one (8) are described. The influence of methyl substitution and benzannelation upon the structure and tropicity of the tetradehydro[13]annulenone 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) and (5).