(3 + 2) Cycloaddition Reaction of the Endocyclic N -Silyl Enamine and N , N' -Cyclic Azomethine Imine.

We describe the (3 + 2) cycloaddition reaction of endocyclic N -silyl enamines and N , N' -cyclic azomethine imines. This process utilized the versatile endocyclic N -silyl enamine intermediates from the dearomative hydrosilylation of N -heteroarenes. The resulting tetracyclic pyrazolidinone structure was synthesized by a straightforward and atom-economical process. We also discussed the plausible origins of the different reactivity and endo/exo selectivity in terms of the structures of each proposed transition state. The successful gram-scale synthesis demonstrated the synthetic utility.