DIMERIC ALPHA-LITHIO-2,6-DIMETHYLSTYRENE

Improved preparations of 2,6-dimethylstyrene (5) and its alpha-bromo d erivative (10) are described. The Br/Li exchange reaction of 10 provid es single crystals of the title compounds 11 or 12, which were charact erized as disolvated dimers by X-ray analyses. A similar dimer persist s in diethyl ether, tert-butyl methyl ether, and toluene at all access ible temperatures, with significant lithiation NMR shifts (relative to 5) partially due to charge delocalization from the sp(2)-carbanionic center. Some NMR coupling constants are typical of the dimeric aggrega te. The configurational (E,Z) lability is quantified in toluene soluti on.