(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.

Synthesis of Cyclic Amidines from Quinolines by a Borane-Catalyzed Dearomatization Strategy.

Described herein is the development of a new synthetic route to cyclic amidines from quinolines. The borane-catalyzed 1,4-hydrosilylation of quinoline was utilized for the dearomatization of the quinolines. The dearomatized enamine intermediate was subsequently reacted with a broad range of organic azides to produce the corresponding cyclic amidines (3,4-dihydroquinolinimines) via a [3 + 2] cycloaddition pathway. Preliminary mechanistic studies suggested that the hydride shift was involved during the cycloaddition.