Access to Spiro and Fused Indole Derivatives from α,β-Unsaturated Aldehydes Enabled by N-Heterocyclic Carbene Catalysis

Spiro and fused indoles are attractive heterocyclic compounds with broad and promising activities in various therapeutic fields, and thus, have become the synthetic targets of organic chemists. In this account, we describe our recent progress in the synthesis of a series of spiro and fused indole derivatives through N-heterocyclic carbene (NHC)-catalyzed annulations of diverse NHC-bound intermediates derived from α,β-unsaturated aldehydes. Particularly, the novel synthesized isatin-derived α-bromoenals may be used as versatile 1,3-biselectrophile synthons for combination with a range of bisnucleophiles for potentially divergent syntheses of skeletally diverse spirooxindoles in the future.