Efficient Direct and Modular Stereoselective Synthesis of Highly Functionalized Tetrahydroisoquinolines and C2-1,1′-Bitetrahydroisoquinolines

An efficient modular stereoselective synthesis of highly functionalized tetrahydroisoquinolines and C 2 -1,1′-bitetrahydroisoquinolines chiral ligands is disclosed. The synthetic methodology relies on direct stereoselective Pictet–Spengler cyclization between ( S )-4-benzyloxazolidin-2-ones and various mono- and dialdehydes using inexpensive sulfuric acid as the catalyst.