Synthesis of Spirolactams and Fused Bicyclic Lactams via Acid-Promoted Cyclolactamization of (Ethynyl(tosyl)amino)methyl-Tethered Cyclohex-2-enols

A simple
synthetic method to construct the spirolactam framework
from TfOH-catalyzed spirolactamization of cyclohex-2-enols bearing
a tethered (arylethynyl­(tosyl)­amino)­methyl moiety is described. The
reaction proceeded through a keteniminium–allylic carbocation
intermediate. Hydration of the keteniminium ion, followed by attack
of the resulting enolate onto the tethered allylic carbocation, provided
the spirolactam ring skeleton. This strategy could also be employed
in the synthesis of fused bicyclic lactams from BF3·OEt2-assisted cyclolactamization of TBS-protected 2-(ethynyl­(tosyl)­amino)­methylcyclohex-2-enols.