Temperature and Solvent Effect on the Nucleophilic Addition of n ‐Butyllithium to the N ‐(Trimethylsilyl)imine of (2 S )‐Lactal

Are the Felkin–Ahn and Cram chelate models reliable? These models predict asymmetric induction without consideration of solvent and temperature. However, the addition of n ‐butyllithium to the N ‐(trimethylsily)imine of (2 S )‐lactal leads to syn/anti ratios between 98:2 and 28:72 when performed in different solvents and at different temperatures. The reaction appears to be the first example of nucleophilic addition that follows the isoinversion principle (isoinversion temperature T i = −21 °C). This indicates a stepwise process with at least two diastereoselective steps that are affected differently by temperature and solvent.