Vinylogous Reactivity of Oxindoles Bearing Nonsymmetric 3‑Alkylidene Groups

The
γ-functionalization of oxindoles bearing nonsymmetric 3-alkylidene
groups via vinylogous Michael-type addition to nitroolefins
was realized. The suppression of the interconversion between the E and Z isomers of the starting oxindoles
allowed a site-specific diastereoselective and enantioselective transformation.
Specific experiments allowed us to establish the rate-determining
step of the reaction and to advance a robust hypothesis for the
exclusive formation of an s-cis enolate as the only
reactive intermediate.