W Tungsten

Benzothiazoline better than Hantzsch: A stereoselective Brønsted acid catalyzed reductive amination/aza-Michael approach towards the important class of tetrahydroisoquinolines is presented (see scheme). A biphenyl-substituted benzothiazoline is used as reducing agent and led to superior yields and enantiomeric excesses compared to the frequently used Hantzsch ester. The cyclization of the amine intermediate occurs smoothly with potassium tert-butoxide as base and affords the trans-1,3-disubstituted tetrahydroisoquinolines.