NHC-Catalyzed Asymmetric Photoinduced [4 + 2] Cycloaddition: Access to Chiral Spiro[oxindole-3,4'-pyrano[2,3-c]pyrazoles].

A N-heterocyclic carbine (NHC)-catalyzed photoinduced asymmetric [4 + 2] cycloaddition reaction has been established for the efficient construction of chiral spiro[oxindole-3,4'-pyrano[2,3-c]pyrazole] derivatives in moderate to high yields (52-97%) with outstanding stereocontrol (up to >20:1 dr and >99% ee). This facile protocol features a broad substrate scope and the rapid assembly of vicinal bis-chiral quaternary carbon centers. Furthermore, the resulting chiral compounds exhibit promising antitumor activity against breast cancer.