Aldehyde-Assisted Oxidative [3 + 2] Cascade Annulation of Indolecarbaldehydes with Alkynes: Access to Cyclopenta[b]indol-1(4H)-one and Spirooxindole Derivatives

A rhodium-catalyzed aldehyde-directed oxidative [3 + 2] cascade annulation of indolecarbaldehydes with alkynes has been developed to deliver cyclopenta[b]indol-1(4H)-one. This protocol is compatible with electronically diverse substituted indole aldehydes and symmetrical diarylacetylenes, affording products in moderate to excellent yields (up to 88%). The resulting cyclopenta[b]indol-1(4H)-one can be further transformed into spiro[furan-2,2'-indoline]-3',5-dione, which displayed blue or green emission properties, with compound 4c exhibiting a distinct solvatochromic effect in different solvent.