Synthesis and properties of a trimethyltetradehydro[17]annulenone and its benzannelated derivatives

Abstract

Syntheses of 2,7,12-trimethyl-8,9,10,11-tetradehydrocycloheptadecenone (5), 10,15-(6) and 8,15-dimethyl-16,17,18,19-tetradehydrobenzocycloheptadecen-9-one (7), and 8-methyl-18,19,20,21-tetradehydrodibenzo[a,g]cycloheptadecen-9-one (8) are described. The ¹H n.m.r. spectra of these annulenones and related compounds indicate that the skeleton of the tetradehydro[17]annulenone ring system is more planar and less strained than that of the corresponding [13]annulenones.