A new route to 2-spiropiperidines

An intramolecular Mannich reaction, involving cyclanones together with a ketoprotected aminobutanone in the presence of a Lewis acid, is employed to prepare rapidly 2,2′-spiropiperidine skeletons. This approach is validated through a concise and efficient synthesis of spiro [piperidine-2,2′-adamantane] 4, an antiviral agent.