Preperations and Reactions of Symmetrical Dimethylenebiphenyl Dianions; Conformations of -o-Cyclophanes. A Simple NMR method for Determining Twist Angles in Biphenyls

Article abstract of DOI:10.1021/jo00263a011

With n-butyllithium / potassium tert-butoxide, a proton is removed from each methyl group of the symmetrical dimethylbiphenyls to give dianions in good yield.The reactions of these dianions with alkyl halides, dialkyl sulfates, trimethylchlorosilane, trimethylchlorogermane, α,ω-dihalides, and oxidizing agents were found to provide the best routes to many symmetrically substituted biphenyls, including <0.n>- and <0.n.0.n>cyclophanes.NMR and molecular mechanical studies of some of these cyclophanes gave information on their preferred conformations.An NMR method for determining the angle of twist in biphenyls from the chemical shifts of the ortho hydrogens is developed.