Syntheses and properties of a trimethyltetradehydro[23]annulenone and a trimethyltetradehydro[25]annulenone

The syntheses of 2,9,14-trimethyl-10,11,12,13-tetradehydrocyclotricosenone (6) and 2,11,16-trimethyl-12,13,14,15-tetradehydrocyclopentacosenone (7) are described. Examination of the 1H n.m.r. spectra indicates that (6) is diatropic, whereas (7) is paratropic, and these ring currents are increased by dissolution in deuteriotrifluoroacetic acid.