Stereoselective formal [3 + 3] annulation of 3-alkylidene-2-oxindoles with β,γ-unsaturated α-keto esters

Switchable Chemoselectivity in [3 + 3] Annulation of β,γ-Unsaturated α-Ketoesters and 1H-Pyrazol-5-amines by Cooperative Acid Catalysis with NiII and InI

The exchange of the metal ion from Ni(II) to In(I) leads to a switch in the chemoselectivity of the [3 + 3] annulation of β,γ-unsaturated α-ketoesters and 1H-pyrazol-5-amines in the presence of phosphoric acid 1, affording functionalized 1H-pyrazolo[3,4-b]pyridines 4 in up to 97% yields and highly enantioselective 4,5-dihydro-1H-pyrazolo[3,4-b]pyridines 5 in up to 92% yield and 99% ee.

Asymmetric (3 + 3) and (4 + 2) Annulation Reactions of 2,3-Dioxopyrrolidines with 3-Alkylidene Oxindoles to Construct Diverse Chiral Heterocyclic Frameworks

Two substrate-controlled regiodivergent annulation protocols for 2,3-dioxopyrrolidines with 3-alkylidene oxindoles have been developed, which furnished a series of fused dihydropyrrolidone derivatives in high yields with excellent stereoselectivities. Plausible mechanistic pathways for both annulation reactions are proposed that [3 + 3] annulation reaction involves vinylogous Michael addition followed by intramolecular aldol cyclization, while [4 + 2] annulation reaction occurs through a vinylogous Michael addition and a subsequent intramolecular oxa-Michael cyclization.