A Convenient Synthesis of 1,1-Disubstituted 1,2,3,4-Tetrahydroisoquinolines via Pictet-Spengler Reaction Using Titanium(IV) Isopropoxide and Acetic-Formic Anhydride.
A synthesis of 1,1-disubstituted 1,2,3,4-tetrahydroisoquinolines (6) was achieved in a highly efficient manner via Pictet-Spengler reaction of arylethylamines (1) and acyclic and cyclic ketones (2) using titanium (IV) isopropoxide and acetic-formic anhydride. The cyclization of the in situ formed acyliminium ion (4) to N-formyl 1,2,3,4-tetrahydroisoquinoline (5) was greatly facilitated by using trifluoroacetic