The lithiation and asymmetric substitution of N-(2-phenylethyl)isobutyramide (2) with selectedelectrophiles, under the influence of (−)-sparteine, provides benzylically substituted products in58−90% yields with enantiomeric ratios (ers) from 72:28 to 91:9. Syntheses of enantioenricheddihydroisoquinolines (S)-18 and (S)-19 and a tetrahydroisoquinoline (4S)-20 provide examples ofsynthetic applications. Mechanistic investigations suggest the enantiodetermining step at −78 °Cis a dynamic thermodynamic resolution.