Preferential crystallization of (±)-pinenyllithium·TMEDA.

ABSTRACT

(±)-Pinenyllithium·TMEDA or (tetramethylethylenediamine-κ2N,N')(η3-6,6-dimethyl-2-methylenebicyclo[3.1.1]heptyl)lithium, [Li(C10H15)(C6H16N2)], is readily prepared from ß-pinene, butyllithium and TMEDA, and the racemic material preferentially crystallizes even from 964 (92% ee) mixtures of (-)- and (+)-ß-pinene, respectively. The structure is monomeric, with the geminal-dimethyl bridge of the bicyclic structure shielding one face of the allyl system, restricting the lithium to the opposite face and preventing the Li-allyl-Li aggregation observed with some other allyllithium systems. The symmetry of the allyl system, bond lengths, bond angles and out-of-plane deviations are compared to existing structures. In addition, a much older structure of this complex is compared to this very recent one.