Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions

A novel one‐pot, three‐component diastereo‐ and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β‐unsaturated pyrazolones, which react with a second equivalent of enal through an N‐heterocyclic carbene (NHC)‐catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3‐diketones, 2,5‐chromenediones are available through [2+4] annulation. Aldol/NHC cooperation: Three‐component, one‐pot, aldol condensation/N‐heterocyclic carbene (NHC)‐catalyzed [3+2] annulation reations have been developed to steroselectively assemble spiropyrazolones through an azolium homoenolate pathway. By simply replacing the pyrazolones by diketones, highly substituted 2,5‐chromenediones are obtained through a [2+4] annulation reaction by an azolium enolate route.