Three complementary methods offering access to 5-substituted 1,2,3,4-tetrahydroisoquinolines

The scope and limitations of three independent though related routes leading to 5-substituted tetrahydroisoquinolines are explored : the Pidet-Spengler type cyclization of ortho-substituted 2-phenylethylamines, the Pomeranz-Fritsch type cyclization of meta-substituted benzylamines and the electrophilic trapping of 5-lithiated 4-lithiooxytetrahydroquinolines. The introduction of the substituent relies in all three cases on a neighboring group assisted site selective metalation step. (C) 1998 Elsevier Science Ltd. All rights reserved.