Syntheses and properties of trimethyltetradehydro[19]annulenones and the benzannulated derivatives

Abstract

Syntheses of 2,7,12-(5) and 7,12,19-trimethyl-8,9,10,11 -tetradehydrocyclononadecenone (6),17-methyl-18,19, 20,21 -tetradehydrobenzocyclononadecen-11-one (7), and 8-methyl-20,21,22,23-tetradehydrodibenzo[a,g]cyclononadecen-9-one (8) are described. The influence of α-methyl substitution and benzannulation upon the structure and tropicity of the tetrahydro[19]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 7,12-dimethyl-8,9,10,11-tetradehydrocyclononadecenone (4).