Rh(III)-Catalyzed Mild Coupling of Nitrones and Azomethine Imines with Alkylidenecyclopropanes via C–H Activation: Facile Access to Bridged Cycles

Bridged cycles are an important class of structural motif in various biologically active molecules. Rh(III)-catalyzed C–H activation of nitrones and azomethine imines in the context of dipolar addition with alkylidenecyclopropanes (ACPs) have been realized. By taking advantage of the ring strain in ACPs, the reaction with aryl nitrones delivered bridged [3.2.1] bicyclic isoxazolidines, and reaction with azomethine imines afforded bridged tricyclic pyrazolones under the same conditions, where both the nitrone and azomethine imine act as a dipolar directing group. All the reactions occurred under mild conditions with broad substrates scope, high efficiency, and >20:1 diastereoselectivity. The synthetic applications of this protocol have also been demonstrated.