Asymmetric Synthesis of Spiropyrazolones by Rhodium-Catalyzed C(sp2 )-H Functionalization/Annulation Reactions.

Rhodium-catalyzed C(sp2 )-H functionalization reactions of 4-aryl-5-pyrazolones followed by [3+2] annulation reactions with alkynes provide rapid access to highly enantioenriched five-membered-ring 4-spiro-5-pyrazolones. The use of a chiral SCpRh catalyst enabled the synthesis of a large range of spiropyrazolones with all-carbon quaternary stereogenic centers in up to 99 % yield and 98 % ee from readily available substrates.