Newly intramolecular α-amidoalkylation cyclisation: Use of the N- acyliminium ion with a sulfur atom as a nucleophile

Article abstract of DOI:10.1016/S0040-4039(99)00484-0

Pyrrolidino(or isoindolo)[1,3]benzothiazines 1 a,b were efficiently synthesized in a four-step sequence from the known o-(benzylthio) benzyl alcohol 2. The key step was the nucleophilic attack of the sulfur atom onto N-acyliminium ion 6 which was generated in high acidic medium from ω- carbinol lactam 5. The last was regioselectively obtained by reduction of the parent imide 4.