Syntheses of 9-Substituted 1-methylfluorene Derivatives and Restricted Rotation around the C(9)-C Single Bonds in these Compounds

Abstract

Reaction of 1-methyl-9-fluorenone [ 1 ] with a variety of Grignard reagents or organolithium compounds gave 9-substituted 1-methyl-9-fluorenols [ 4].9-Alkoxy-9-ary1-1-methylfluorenes [6 ] were obtained by refluxing the solution of 9-bromo-1-methylfluorenes [ 5 ] in alcohol which in turn were prepared from C 4 J with HBr in acetic acid. Reduction of [ 4 ] with HI in acetic acid gave 9-substituted 1-methylfluorenes [ 7 ] (e. g., 9- (2-methylpheny1)- [7 e], 9- (3- methylpheny1)- [7 f], 9- (4-methylphenyl) - [7 g], 9- (1-naphthyl) [7 h], and 9- (2-methyl-1-naphthyl)-1-methylfluorene [7 i]).
The restricted rotation around the C_sp3-C_sp2 single bond in [ 7 ] has been investigated by means of the DNMR method. Rotational barriers around the C_sp3-C_sp2 bond in [7 e] (Δ G_115c=19.6 kcal/mol) and [7 h] (Δ G_160o=21.4 kcal/mol) were found to be 2-3 kcal/mol higher than those of 9- (2-methylphenyl)fluorene and 9- (1-naphthyl) fluorene, respectively.