Diastereoselective Protonation of Lactam Enolates Derived from (<i>R</i>)-Phenylglycinol. A Novel Asymmetric Route to 4-Phenyl-1,2,3,4-tetrahydroisoquinolines

Highly diastereoselective protonation of chiral lactam enolates of 4-substituted-1,4-dihydroisoquinolin-3-ones is reported. Protonation and alkylation processes of these lactam enolates derived from phenylglycinol occur with opposite diastereofacial selectivity. This diastereoselective protonation has been applied to the asymmetric synthesis of (4<i>S</i>)-<i>N</i>-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline <b>9</b> obtained in up to 97% ee.