Diastereoselective Construction of Tetrahydro-Dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] Scaffolds via an Oxa-Michael Cascade [4 + 2] Annulation Reaction.

A straightforward metal-free oxa-Michael cascade [4 + 2] annulation reaction was established between isatin-derived Morita-Baylis-Hillman (Is-MBH) alcohols with alkylidene pyrazolones to access structural diverse tetrahydro-dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] scaffolds bearing two tertiary and two quaternary stereocenters. The Is-MBH alcohol was utilized as an oxa-Michael donor for the first time as a new approach in highly atom-economical transformations. This method offered a wide range of bioinspired novel tetrahydro-dispirooxindole-pyran-pyrazolone derivatives in excellent yields (up to 96%) and diastereoselectivities (up to >20:1) in a shorter reaction time (15 min).