A dual catalytic reaction is a way of organic synthesis in which two catalysts are used to react to a chemical reaction to give rise to new or more efficient reactions. This scheme may be a combination of two independent catalysts, e.g., a photocatalyst and a metal catalyst, or a sequence of catalysts, e.g., a relay or cooperative catalysis system. The current study presents a sustainable synthetic methodology of synthesizing azaarene-substituted 3-hydroxy-2-oxindoles through sp3 C-H functionalization, as well as a complementary metal-free sulfono functionalization methodology of benzyl and alkyl halides, and methylarenes. It employs the TBAF- 3H2O as an effective organocatalyst in a water system under microwave irradiation to catalyze sp3 C-H activation of alpha/gamma-alkylazaarenes and alpha-alkylquinolines with high yield. The reaction parameters were optimized to show that at 100 C, 10 mol% TBAF- 3H2O catalyst gave up to 90% of the target 3-hydroxy 2-oxindoles. It was also extended to a range of isatin analogues, which afforded a range of azaarene-substituted oxindoles in good to excellent yields. It is concluded that the study successfully demonstrates two sustainable methodologies for synthesizing functionalized heterocyclic compounds.
Kumar et al. (Tue,) studied this question.