Chiral N‐Heterocyclic Carbene/Squaramide‐Cocatalyzed Asymmetric Intramolecular Stetter Reaction to Construct Benzo‐Fused Spiro[4.5]Decanedione Framework

An N‐heterocyclic carbene (NHC)/squaramide‐cocatalyzed asymmetric intramolecular Stetter reaction is described. Various cyclopentenone‐benzaldehydes were exposed to a chiral NHC and a chiral squaramide, whereupon the intramolecular Stetter reaction proceeded smoothly at room temperature to give the corresponding benzo‐fused spiro[4.5]decanedione skeletons in 49%–71% yields with 44%–81% ee.