Sparteine-mediated asymmetric nucleophilic substitution at prochiral, sp(3)-hybridized carbon.
[reaction: see text] ++-Phenyl-1,3-dioxolanes (1) react with organolithium reagents (2), associated with (-)-sparteine, in the presence of BF(3).OEt(2) to afford chiral monosubstitution products 3. Enantioselectivity is highest if both 1 and 2 carry alkyl substituents in the ortho position. However, the enantioselectivity decreases in the case of very bulky substituents such as tert-butyl or phenyl.
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Department of Organic Chemistry, University of Geneva, 30, Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland. paul.muller@chiorg.unige.ch
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