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.