5-Aryloxazolidines react with arenes under Lewis or Brønsted acid conditions via the Friedel-Crafts/Pictet-Spengler double alkylation sequence to give alkaloid-like 4-aryltetrahydroisoquinolines in 12-94% yields. Three approaches for the controlled insertion of substituents into the target molecules and application of oxazolidine derivatives such as 1-arylethanol-2-amines or 4-hydroxytetrahydroisoquinolines in the alkylation of arenes are also described. An unprecedented two-step easily scalable synthesis of the 4-aryltetrahydroisoquinoline core from aromatic aldehyde was achieved applying oxazolidine methodology.