Asymmetric syntheses by means of (−)-sparteine modified organometallic reagents

Asymmetric induction has been observed in the reactions of organo-lithium and magnesium compounds complexed with a chiral tertiary diamine, (−)-sparteine. Debromination of gem-dibiomocyclopropanes with such complexed n-BuLi gives optically active allenic hydrocarbons, and this shows that the intermediate leading to allene is lithium carbenoid (or α-bromocyclopropyllithium) rather than free cyclopropylidene. Addition of organolithium or a Grignard reagent to carbonyl compounds proceeds dissymmetrically to afford carbinols of up to 22% optical purity. Finally lithiation of ethylbenzene with n-BuLi has been examined in the presence of (-⊃-sparteine and the resulting α-phenethyllithium complex yields optically active products.