Enantioselective Lithiation and Substitution of (E)-CinnamylN,N-Diisopropylcarbamate through Use of (−)-Sparteine Complexes

The title reaction leads to diastereomeric lithium carbanion pairs that are configurationally unstable and equilibrate even at temperatures below –50 °C. The initially formed epimer (1S)-epi-10 is rapidly converted to the thermodynamically more stable (1R)-10 (in toluene solution). Carboxylation, acylation with acid chlorides, stannylation, and silylation take place at the α-position with stereoinversion (79-86% ee). Methylating agents attack the γ-position; here, the stereochemical course depends on the leaving group, anti-SE′ for the iodide (50% ee) and syn-SE′ (48% ee) for the tosylate.