Diversity-Oriented Preparation of Enantiopure Spirocyclic 2-Azetidinones from α-Oxo-β-lactams through Barbier-Type Reactions followed by Metal-Catalyzed Cyclizations

Novel, simple, and convenient strategies to diversely functionalized spirocyclic β‐lactams have been developed by using different metal‐mediated carbonyl addition/cyclization reaction sequences. Spirocyclization precursors, 2‐azetidinone‐tethered homoallylic alcohols, bromohomoallylic alcohols, homopropargylic alcohols, (buta‐1,3‐dien‐2‐yl)methanols, and α‐allenols have been obtained by regioselective addition of stabilized organometallic reagents to azetidine‐2,3‐diones in an aqueous environment. Ruthenium‐, silver‐, and palladium‐catalyzed reactions of the above monocyclic unsaturated alcohol derivatives provided oxaspiro‐β‐lactams.