Treatment of several amido-substituted thioacetals with dimethyl (methylthio) sulfonium tetrafluoroborate (DMTSF) produces synthetically useful thionium ions that are intercepted by the adjacent nitrogen atom to afford both five-and six-membered alkylthio-substituted lactams as transient intermediates. Further reaction of the alkylthio-substituted lactam with DMTSF generates an N-acyliminium ion, which undergoes cyclization with the tethered ...
