TBD-Mediated Diastereoselective\nAccess to Functionalized\n3‑Alkenyl-2-oxindoles via the Tandem Reaction of Isatins and\nAllenoates

The 1,5,7-triazabicyclo[4.4.0]dec-5-ene–mediated\ntandem\nreaction of easily accessible isatins and allenoates to functionalized\n3-alkenyl-2-oxindoles is disclosed. The reaction allows the synthesis\nof a wide range of 3-alkenyl-2-oxindoles in good yields with excellent\nfunctional group tolerance under mild reaction conditions (32 examples,\nup to 84% yields). The current strategy will provide a novel path\nfor the sustainable synthesis of functionalized 3-alkenyl-2-oxindole\nderivatives. We have also demonstrated the significance of 3-alkenyl-2-oxindoles\nas key starting materials (KSMs) via their synthetic utility in producing\noxindole-appended pyrazole, oxazole, and coumarin hybrids of medicinal\nrelevance.