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

Abstract 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.