Asymmetric Synthesis of Arylglycines and Their Use as Chiral Templates for the Stereocontrolled Synthesis of 7,8-Disubstituted 3-Aryl-1,2,3,4-tetrahydroisoquinolin-4-ols

A synthetic technique for the asymmetric synthesis of arylglycines has been optimized, reaching the target amino acids in only four steps with good yields and with enantiomeric excesses higher than 99%. The key step consisted of a stereocontrolled electrophilic amination reaction of (S,S)-(+)-pseudoephedrine-based arylacetamide enolates with di-tert-butylazodicarboxylate. The arylglycines thus obtained turned out to be excellent chiral templates for the production of chiral, nonracemic 7,8-disubstituted 3-aryl-1,2,3,4-tetrahydroisoquinolines, through use of a synthetic sequence involving: (1) reduction of the arylglycines to the parent arylglycinols, (2) N-benzylation with appropriately substituted aromatic aldehydes and (3) Swern oxidation followed by acid-catalysed cyclization of the obtained α-amino aldehydes.