Alkynylation of Isatin Derivatives Catalyzed by a Silver-Chiral Quaternary Ammonium Salt Derived from Quinine.

Asymmetric addition of terminal alkynes catalyzed by a transition metal to isatins obviously is an efficient and economic method for the synthesis of 3-alkynyl-3-hydroxy-2-oxindoles. The new dimeric chiral quaternary ammoniums derived from a natural chiral alkaloid, quinine, can be used as cationic inducers of the enantioselectivity for the Ag(I)-catalyzed alkynylation of isatin derivatives under mild conditions. The desired chiral 3-alkynyl-3-hydroxy-2-oxindoles can be obtained in good to high yields with high to excellent enantioselectivites (≤99% ee). A variety of aryl-substituted terminal alkynes and substituted isatins are tolerated in this reaction.