SYNTHESIS OF CHIRAL ALPHA-SUBSTITUTED -[((2S)-2-HYDROXY-2-PHENYL)-ETHYL]-2-PHENYLGLYCINE DERIVATIVES BY DIASTEREOCONTROLLED ALKYLATION OF 'R)-(2'-METHYL)PHENYL-METHYL]-4H-1,4-OXAZIN-2-ONES

The synthesis of a-substituted N-[((2S)-2-hydroxy-2 phenyl)-ethyl]-2-p henylglycine derivatives is reported. The key step of the sequence is the highly diastereoselective alkylation of 2'R)-(2'-methyl)phenylmeth yl]-4H-1,4-oxazin-2-ones after deprotonation with t-BuOK. Opening of t he resulting oxazinone with ethanolic KOH, followed by hydrogenolysis of the corresponding N-[(2R)-(2-methyl)phenylmethyl] compound to furni sh the expected 2-phenylglycine derivative, is also described. (C) 199 7 Elsevier Science Ltd.