Enantioselective synthesis of 1-substituted tetrahydroisoquinoline-1-carboxylic acids

The 3,4-dihydroisoquinolinium salt 1 and its enantiomer have been converted readily and stereoselectively into (+)-and (−)-1,2,3,4-tetrahydro-6,7-dimethoxy-1-methylisoquinoline-1-carboxylic acids. The synthetic route described should be applicable to the enantioselective synthesis of a variety of 1-alkyl- or 1-aryl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acids. The absolute configuration of the amino acid hydrochloride 11 was established to be as depicted in Scheme 2.