Synthesis of 9-Ary1-1,8-dihalogenofluorene derivatives and their conformational equilibria

The compounds, 1,8-difluorofluorenone (9), 1,8-dibromofluorenone (10) and 1,8-diiodofluorenone (11) were prepared from fluorene as starting material via 9 steps. The reaction of 9 and 10 with 2-methyl-phenyllithium in ether gave 1,8-difluoro-9-(2-methylphenyl)-9-fluorenol (12) and 1,8-dibromo-9-(2-methylphenyl)-9-fluorenol (13), respectively. Then, 12 and 13 were reduced by HI/AcOH into 1,8-difluoro-9-(2-methylphenyl) fluorene (14) and 1,8-dibromo-9-(2methylphenyl) fluorene (15). The conformational equilibria of these 9-aryl-1,8-dihalogenofluorene derivatives (12)-(15) between ap-and sp-forms were investigated, and then activation parameters for the internal rotation and equilibrium constants of 14 and 15 were measured, and compaired with that of known 1,8-disubstituted 9-(2-methylphenyl) fluorene derivatives. Thus, the existence of attractive interaction between 1,8-dihalogeno substituents and CH_3 of 2-methylphenyl group was presumed in sp forms of 14 and 15.