Enantioselective Synthesis of Dihydrospiro[indoline-3,4′-pyrano[2,3‑<i>c</i>]pyrazole] Derivatives via Michael/Hemiketalization Reaction

A new bifunctional squaramide organocatalyst derived from l-proline mediated the first enantioselective synthesis of dihydrospiro­[indoline-3,4′-pyrano­[2,3-<i>c</i>]­pyrazole] derivatives in excellent enantioselectivity by reacting pyrazolones with isatylidine β,γ-unsaturated α-ketoester. This new catalyst outperformed widely used thioureas and squaramides in inducing enantioselectivity

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)

Diastereo- and Enantioselective Synthesis of 2,2-Disubstituted Benzofuran-3-one Bearing Adjacent Quaternary and Tertiary Stereocenters

The first highly diastereo- and enantioselective synthesis of armeniaspirol analogues was achieved using L-proline derived bifunctional squaramide which outperformed commonly used organocatalysts. Excellent yield (up to 99%) with diastereoselectivity (up to 99:1) and enantioselectivity (up to 99%) were obtained for a wide range of substrates

Palladium Catalyzed Asymmetric Allylation of 3‑OBoc-Oxindoles: An Efficient Synthesis of 3‑Allyl-3-hydroxyoxindoles

3-Allyl-3-hydroxyoxindoles were synthesized in very good enantio- (up to 97% ee) and diastereoselectivities (dr up to 7.6:1) with contiguous quaternary and tertiary stereogenic centers by employing tartrate derived bi­(oxazoline) in Pd-catalyzed allylation of 3-OBoc-oxindole. Synthetic utility of 3-allyl-3-hydroxyoxindole was demonstrated by synthesizing a highly substituted spiro­(oxindole-3,2′-tetra­hydro­furan) derivative in good yield and stereoselectivity