N-Heterocyclic Carbene-Catalyzed Annulations of Enals and Ynals with Indolin-3-ones: Synthesis of 3,4-Dihydropyrano[3,2-b]indol-2-ones

Enal and ynal-derived α,β-unsaturated acylazoliums under N-heterocyclic carbene (NHC) catalysis have been applied for annulations with indolin-3-ones. The two reactions offer a direct and efficient access to functionalized 3,4-dihydropyrano[3,2-b]indol-2-ones in moderate to high yields, which may provide promising candidates for drug discovery.