Intramolecular Pictet–Spengler Reaction of Cyclic Iminium Ions: A Novel Access to Benzo[1,4]oxazepine‐Fused Tetrahydroisoquinoline and Tetrahydro‐β‐carboline Analogues

A simple and efficient approach has been developed for the synthesis of benzo[1,4]oxazepino-fused tetrahydroisoquinoline and tetrahydro-beta-carboline derivatives via one-pot cascade reaction sequence. This reaction involves the intramolecular Pictet-Spengler reaction of cyclic iminium ions, which were generated in situ via trifluoroacetic acid (TFA)-mediated deprotection of an acetal derived from beta-arylethylamines and 2-(2,2-diethoxyethoxy)benzaldehyde. All reactions produced a novel library of complex fused polyheterocyclic compounds in good to excellent yields.