In conclusion, we have successfully developed an unprecedented cascade approach using mild conditions to access complex tetrahydro-3,4'-biisoquinolines. The keystone of the present cascade process is the successive formation of two iminium intermediates resulting in the formation of 3 new bonds, therefore allowing creation of molecular complexity and diversity starting from simple substrates. The series of tetrahydro-3,4'-biisoquinoline reported in this work represent potential useful substrates for different fields of chemistry and promising molecules of biological interest. EXPERIMENTAL SECTION General comments. Unless otherwise indicated, common reagents or materials were obtained from commercial source and used without further purification. Tetrahydrofuran (THF) and Dichloromethane (CH2Cl2) was dried by a PureSolv TM solvent drying system. Flash column chromatography was performed using silica gel 60 (230-400 mesh). Analytical thin layer chromatography (TLC) was carried out on Merck silica gel plates with QF-254 indicator and visualized by UV or KMnO4. H and 13 C NMR spectra were recorded on an Agilent DD2 500 (500 MHz 1 H; 125 MHz 13 C) or Agilent DD2 600 (600 MHz 1 H; 150 MHz 13 C) or Agilent DD2 400 (400 MHz 1 H; 100 MHz 13 C) spectrometer at room temperature. Chemical shifts were reported in ppm relative to the residual CDCl3 ( 7.26 ppm 1 H;  77.00 ppm 13 C), CD3OD ( 3.31 ppm 1 H;  49.00 ppm 13 C), or d 6 -DMSO ( 2.50 ppm 1 H;  39.52 ppm 13 C). NMR chemical shifts were expressed in ppm relative to internal solvent peaks, and coupling constants were measured in Hz. (bs = broad signal).