Formal [3+2] Cycloaddition of Nitrosoallenes with Carbonyl and Nitrile Compounds to Form Functional Cyclic Nitrones

The
synthesis of functional cyclic nitrones via [3+2] cycloadditions
of allenamide-derived nitrosoallenes with carbonyl/nitrile compounds,
including ketones, esters, and nitriles, is presented herein. Rapid
carbon–carbon, carbon–oxygen, and carbon–nitrogen
bond formations were achieved with in situ prepared
nitrosoallenes, and densely substituted oxacyclic and carbocyclic
nitrones containing tetrasubstituted carbon centers were successfully
synthesized. The spirocyclic nitrone products synthesized from cyclic
dicarbonyl compounds underwent the unique skeletal rearrangements
to cyclic α-ketonitrones.