Evaluation of N‐Hydroxymethylphthalimide in Alkaline Medium: Novel Entry to the Tricyclic [1,3]Oxazepine Core via an Intramolecular π and O‐Cationic Cyclization.

Abstract

Fused isoindolo [1,3]benzo(or thieno)oxazepines 8a,b and one of their positional isomers aromatic tricyclic N,O-acetals 13b are reported to occur efficiently in a three-step sequence from N-hydroxymethylphthalimide (6). The key step of this methodology is the intramolecular arylation of an endocyclic and/or exocyclic N-acyliminium cation. The mechanism leading to these species, in particular to a tricyclic lactam 13b, is discussed.