Co(III)salen Catalyzed Enantioselective C3‐Indolylation of Spiro‐Epoxyoxindoles and Its Mechanistic Studies

Abstract

Abstract Catalytic asymmetric C3‐indolylation of N ‐protected spiro‐epoxyoxindoles has been developed for the access of 3‐(3‐indolyl)‐oxindole methanols with excellent enantioselectivity (ee up to >99%). The widespread substrate scope and easily accessible Co(III)‐salen over 1,1′‐Spirobiindane‐7,7′‐diol phosphoric acid prove our condition to be more beneficial than the chiral Br ø nsted acid‐catalyzed reaction. Further, kinetic resolution of spiro‐epoxides is achieved in high enantiomeric excess under certain conditions. The detailed mechanistic study endorses that the feedback inhibition played a key role which restricts the dynamic kinetic resolution process. Besides it also revealed the S N 2′ mechanism for the Co(III)‐salen catalysed C3‐indolylation of spiro‐epoxyoxindoles. magnified image