Facile Access to Saccharin‐Fused 1,4‐Dihydropyridines through [3+3] Annulation Reactions

Abstract An efficient approach to saccharin‐fused 1,4‐DHPs has been established by using a [3+3] annulation process. The chemical event was enabled by a Et 3 N‐catalyzed tandem Michael/aza‐Pinner reaction of alkyl cyclic N ‐sulfonyl ketimines as nucleophiles with α , α ‐dicyanoolefins. Under mild conditions, the desired products were readily prepared in good to excellent yields and with broad functional group tolerance (up to 95 % yield, 29 examples). Notably, this practical methodology features the synthesis of pentacyclic spirooxindoles bearing a quaternary spiro‐stereocenter.