Stereoselective synthesis of 3-substituted tetrahydroisoquinolines from phthalan and chiral N-sulfinylimines

The reaction of the dianionic intermediate [resulting from the reductive opening of phthalan (1) with lithium] with chiral N-tert-butylsulfinyl aldimines 3 in the presence of ZnMe₂ gives, after hydrolysis, N-tert-butylsulfinyl amino alcohols 4 with high diastereoselectivity. Successive treatment of compounds 4 with hydrogen chloride in methanol, thionyl chloride in chloroform and sodium hydroxide yields 3-substituted tetrahydroisoquinolines 6.