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Lithiation of biphenyl with 2.4 mol of n-butyllithium in the presence of TMEDA led directly to the 2,2′-dilithio derivative (I) in modest, but preparatively useful yields. I, in turn, was converted to a variety of products. The activation of the 2′-position of 2-lithiobiphenyl was shown directly by a separate experiment. MNDO calculations indicate stabilization in I by double bridging and in 2-lithiobiphenyl by intramolecular π interaction of Li with the o-phenyl group. Similar interactions in substitution transition states rationalize the specificity of the reactions observed.

Due to electrostatic interactions and a contribution of multicenter bonding involving lithium 2s and 2p valence orbital contributions to cyclic 6π delocalization, the doubly bridged cis structure 1 for the title compound is more stable than other alternatives.

The title compounds have been studied by using both molecular mechanics (MMI and MM2) and molecular orbital (MINDO/3, MNDO, and ab initio (3-21G basis)) calculations. The optimum structure is found to be planar in each case, although the energy required for nonplanar distortion is small and decreases regularly with the degree of benzannulation. The large puckering amplitudes to be expected explain the experimentally observed behavior. 4 figures, 1 table.

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution.