Enantioselective Synthesis of Tetrahydroquinoline Alkaloids (-)-Angustureine and (-)-Cuspareine from Chiral tert-Butanesulfinyl Imines

The addition of a Grignard reagent to both enantiomeric N-tert-butanesulfinyl imines derived from 3-(2-bromophenyl)propanal 8 proceeded with high diastereoselectivity. The resulting sulfinamides 9 and 12 were easily transformed into tetrahydroquinoline alkaloids (-)-angustureine (4) and (-)-cuspareine (5) after three steps: N-desulfinylation, intramolecular N-arylation and N-methylation.