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

Abstract

Syntheses of 4,9-dimethyl-13-diphenylmethylene-5,6,7,8-tetradehydrocyclotridecene (7), 4,9-dimethyl-15-diphenylmethylene-5,6,7,8-tetradehydrocyclopentadecene (8), 6,11-dimethyl-17-diphenylmethylene-7,8,9,10-tetradehydrocycloheptadecene (9), and 6,11-dimethyl-19-diphenylmethylene-7,8,9,10-tetradehydrocyclononadecene (10) are described. Although examination of the ¹H n.m.r. spectra suggested that all of the fulvenes (7)—(10) are atropic, the benzannelated derivatives of pentadecafulvene (8), i.e. 13-methyl-7-diphenylmethylene-14,15,16,17-tetradehydrobenzocyclopentadecene (25), 13-methyl-9-diphenylmethylene-14,15,16,17-tetradehydrobenzocyclopentadecene (26) and 7-diphenylmethylene-16,17,18,19-tetradehydrodibenzo[a,g]cyclopentadecene (27) were prepared in order to examine the tropicity of (8) more closely. Comparison of the ¹H n.m.r. spectra of these benzannelated fulvenes (25)—(27) with that of (8) reveals that the nonbenzannelated fulvene (8) is atropic. The influence of benzannelation upon the structure of the molecular skeleton of the tetradehydropentadecafulvene system is also discussed.