Enantioselective organocatalyzed multicomponent Biginelli- and Ugi-like reactions involving isatin

The reactions at the C-3 carbonyl group of isatins transform them into 2-oxindole derivatives, featuring in a large number of compounds with biological activities.1 Going on with our interest in the asymmetric synthesis of 3,3-disubstituted oxindoles2 we are exploring the applicability of organocatalysis, particularly chiral Brønsted acid catalysis,3 in the multicomponent Biginelli- and Ugi-like reactions involving isatin as the carbonyl component. The application of such reactions to ketimines remains to date largely unexplored, due to the hard challenge inherent in the stereocontrolled formation of a quaternary stereogenic center. The Biginelli-like reaction, employing urea and various β-dicarbonyl compounds besides isatin, allowed us to obtain a small library of chiral spiro(indoline-pyrimidine)-diones derivatives (1) in high yields and acceptable enantiomeric excesses. Post-condensation reactions have been performed, increasing the number of potentially useful compounds. On the other hand, starting from isatin-derived imines and isocyanoacetamides, we applied an Ugi-like reaction, affording unprecedented, chiral 3-(amino)-3-(oxazol-2-yl)indolin-2-ones derivatives (2) in good yields. For both reactions, the assignment of the absolute configuration at the new oxindole C-3 stereocenter, as well as computational studies in order to explain the stereochemical outcome, are currently underway. References: 1. Singh, G.S.; Desta, Z.Y. Chem. Rev. 2012, 112, 6104. 2. Lesma, G.; Meneghetti, F. Belstein J. Org. Chem. 2014, 10, 1383. 3. Mahalau, M.; List, B. Angew. Chem. Int. Ed. 2013, 52, 518.