TBD-Mediated Diastereoselective Access to Functionalized 3-Alkenyl-2-oxindoles via the Tandem Reaction of Isatins and Allenoates

The 1,5,7-triazabicyclo[4.4.0]dec-5-ene-mediated tandem reaction of easily accessible isatins and allenoates to functionalized 3-alkenyl-2-oxindoles is disclosed. The reaction allows the synthesis of a wide range of 3-alkenyl-2-oxindoles in good yields with excellent functional group tolerance under mild reaction conditions (32 examples, up to 84% yields). The current strategy will provide a novel path for the sustainable synthesis of functionalized 3-alkenyl-2-oxindole derivatives. We have also demonstrated the significance of 3-alkenyl-2-oxindoles as key starting materials (KSMs) via their synthetic utility in producing oxindole-appended pyrazole, oxazole, and coumarin hybrids of medicinal relevance.