A MODIFIED BISCHLER-NAPIERALSKI PROCEDURE FOR THE SYNTHESIS OF 3-ARYL-3,4-DIHYDROISOQUINOLINES

A modification of the Bischler-Napieralski reaction for the cyclization of (1,2-diphenylethyl)amides to the 3-aryl-3,4-dihydroisoquinolines is presented. Elimination of the amide group as the nitrile via the retro-Ritter reaction is avoided by its conversion to an N-acyliminium intermediate with oxalyl chloride-FeCl3. Removal of the oxalyl group in refluxing MeOH-sulfuric acid provides the 3,4-dihydroisoquinolines in moderate to high yields. The method is also highly effective with (2-phenylethyl)amides.