Synthesis of 6-Azaspiro[4.3]alkanes: Innovative Scaffolds for Drug Discovery

New scaffolds for drug discovery, 6‐azaspiro[4.3]alkanes, have been synthesized in two steps from four‐membered‐ring ketones: cyclobutanone, thienone, N ‐Boc‐azetidinone (Boc = tert ‐butoxycarbonyl), etc. The key transformation was the reaction between electron‐deficient exocyclic alkenes and an in‐situ generated N ‐benzylazomethine ylide.