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-hydroxy-methylphthalimide (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.