Selective Vinylogous Aldol Reactions of β‐Methyl‐Substituted Cyclic Enones with Isatins Catalyzed by DBU and Pyrrolidine to Afford 3‐Substituted 3‐Hydroxyoxindoles

The development of regioselective aldol reactions of β‐methyl‐substituted cyclic enone derivatives with isatins to afford the aldol products with the bond formation at the methyl group of the β‐methyl‐substituted cyclic enone derivatives is described. Catalyst systems composed of DBU and pyrrolidine with DMSO were identified that resulted in the aldol reactions with almost perfect regioselectivities. DBU, pyrrolidine, and DMSO were all required to selectively afford the γ‐position‐reacted aldol products. With the use of this method, the scope of the 3‐substituted 3‐hydroxyoxindole derivatives that can be concisely synthesized was expanded.