Syntheses and properties of dichlorodimethyltetradehydro-trideca-,-pentadeca-, -heptadeca-, and -nonadeca-fulvene, and benzannelated pentadecafulvene derivatives

Syntheses of 13-dichloromethylene-4,9-dimethyl-5,6,7,8-tetradehydroclotridecene (18), 15-dichloromethylene-4,9-dimethyl-5,6,7,8-tetradehydrocyclopentadecene (19), 17-dichloromethylene-6,11-dimethyl-7,8,9,10-tetradehydrocycloheptadecene (20), and 19-dichloromethylene-6,11-dimethyl-7,8,9,10-tetradehydrocyclononadecene (21) are described. Examination of the 1H n.m.r. spectra indicates that all of these fulvenes are atropic. Syntheses of benzannelated derivatives of (19), i.e. 7-dichloromethylene-13-methyl-14,15,16,17-tetradehydrobenzocyclopentadecene (28), 9-dichloromethylene-13-methyl-14,15,16,17-tetradehydrobenzocyclopentadecene (29), and 7-dichloromethylene-16,17,18,19-tetradehydrodibenzo[a,g]cyclopentadecene (30) are also described. The influence of the dichloro substitution at the exocyclic bond of the fulvene, and of benzannelation on the structure of tetradehydropentadecafulvene, is discussed on the basis of the 1H n.m.r. and u.v. spectra of these fulvenes as well as those of the corresponding diphenyl substituted derivatives.