A convenient synthesis of bromopentaarylcyclopentadienes containing methyl or fluorine substituents

The ketones C5(3,5-C6H3Me2)4(O) (5b) and C5-2,5(3,5-C6H3Me2)2(C6H5)2(O) (5c) were prepared and characterized. The pentaarylcyclopentadienols C5(C6H5)4(Ar′)(OH) (Ar′=3,5-C6H3Me2, 6a3; Ar′=2,4,6-C6H2Me3, 6a5; Ar′=3-C6H4F, 6a6; Ar′=3,5-C6H3F2, 6a7), C5(3,5-C6H3Me2)4(Ar′)(OH) (Ar′=3-C5H4Me, 6b2; 3,5-C5H3Me2, 6b3; 3,6-C5H3Me2, 6b4; 2,4,6-C5H2Me3, 6b5; Ar′=3-C6H4F, 6a6; Ar′=3,5-C6H3F2, 6a7; Ar′=2,6-C6H3F2, 6a8) were obtained by reaction of the corresponding Ar′Li with the ketones C5(C6H5)4(O) (5a), or C5(3,5-C6H3Me2)4(O) (5b). The synthesis and characterization of the bromopentaarylcyclopentadienes C5(C6H5)4(Ar′)(Br) (Ar′=3,5-C6H3Me2, 7a3; Ar′=2,4,6-C6H2Me3, 7a5) and C5(3,5-C6H3Me2)4(Ar′)(Br) (Ar′=3-C5H4Me, 7b2; 3,5-C5H3Me2, 7b3; 3,6-C5H3Me2, 7b4; 2,4,6-C5H2Me3, 7b5; Ar′=3-C6H4F, 7a6; Ar′=3,5-C6H3F2, 7a7; Ar′=2,6-C6H3F2, 7a8) containing methyl groups or fluorine atoms on the Ar′ rings are reported. The bromopentaarylcyclopentadienes are isolated as a 1:2:2 mixture of three isomers when Ar and Ar′ are different, except when the latter substituent bears two fluorine or two methyl groups in the ortho positions. In these cases the reaction is regiospecific and provides a unique isomer with the di-ortho-substituted arene located in the β-position with respect to the carbon bearing the bromine atom.