N-Heterocyclic Carbene Catalyzed Formal [3+2] Annulation Reaction of Enals: An Efficient Enantioselective Access to Spiro-Heterocycles
作者:Chang Guo、Michael Schedler、Constantin G. Daniliuc、Frank Glorius
DOI:10.1002/anie.201405381
日期:2014.9.15
A highly enantioselective N‐heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of α,β‐unsaturated aldehydes with azaaurones or aurone generating spiro‐heterocycles has been developed. The protocol represents a unique NHC‐activation‐based approach to access spiro‐heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95 % ee).
carbon center at the C2 position of indole has long been an elusive problem in organic synthesis. Herein, by employing a rationally designed hydrogen‐bonding network activation strategy, for the first time, 2,2′‐pyrrolidinyl‐spirooxindole, which is a valuable and prevalent indole alkaloid scaffold, was directly obtained through a catalyticasymmetric [3+2] cycloaddition reaction with high yields and excellent