Abstract Lateral lithiation of ( S)-4-isopropyl-2-( o-tolyl)oxazoline in diethyl ether followed by the reaction with aldehydes in the presence of TMEDA produced the addition products with stereoselectivities up to 84% de. Utilization of TMEDA as a ligand is essential for the good selectivity. Rationale for the stereoselectivity is proposed based on ab initio calculation of the lateral lithio species. The major ( S, S)-products lactonized faster than the minor ( S, R)-products to the corresponding 3,4-dihydroisocoumarins under acidic conditions. Thus, (3 S)-3,4-dihydroisocoumarins were obtained in good optical purities up to 97% ee by sequential application of these matched stereoselective reactions.