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A novel synthetic method to access fused indolin-3-ones with a tetrasubstituted carbon stereocenter has been developed via NHC-catalyzed umpolung formal [3+3] cycloaddtion of enals with isatogens. This methodology could be also applied for the quick construction of the 6-5-5 tricyclic pyrrolo[1,2-a]indole skeleton which is frequently found as a core structure of many indole alkaloids.

In most cases, the title reactions proceed via a3-d3 umpolung of alkynyl aldehydes (I) and (V) resulting in spirooxindole butenolides (III) and (VI), respectively.

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.

The reaction leads to the stereoselective formation of highly functionalized spirooxindole 4H-pyran-2-ones with three contiguous stereocenters, generally accompanied by small amounts of Knoevenagel products.

A highly efficient atom-economical transition metal-free hydroacylation of isatin derivatives with aromatic and aliphatic aldehydes is described.