An efficient, organocatalyticenantioselectiveaddition of cyclic diketones with β,γ-unsaturated α-keto esters has been developed that affords products in high yields (up to 95 %) and excellent enantioselectivity (up to >99 % ee) under mild conditions with a low catalyst loading (2.5 mol-%). The unsaturated α-keto esters are effectively coordinated and activated through hydrogen bonds with the squaramides
A direct asymmetric Michael addition of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturatedα-ketoesters could be efficiently catalyzed by an N,N′-dioxide–nickel(II) complex. A series of chiral warfarin derivatives were obtained in excellent yields (up to 99%) with high enantioselectivities (up to 90% ee) under mild conditions within shorter reaction time.
Enantioselective Synthesis of Coumarins Catalyzed by a Bifunctional Amine-Thiourea Catalyst
作者:Yaojun Gao、Qiao Ren、Lei Wang、Jian Wang
DOI:10.1002/chem.201002202
日期:2010.11.22
Efficient excess: An efficient and facile enantioselective Michael addition reaction through hydrogen‐bonding catalysis for the synthesis of coumarin complexes has been developed (see scheme). A simple bifunctional amine–thiourea small molecule has been discovered to catalyze this process with high yields and high to excellent enantiomeric excesses.
chiral tridentate bis(pyrroloimidazolone)pyridine (PyBPI) ligands have been designed, synthesized, and applied in an asymmetric Michael addition. With a 0.05 mol % PyBPI–Co(II) complex, β,γ-unsaturated α-keto esters reacted with 4-hydroxycoumarin to give the adducts in 93–99% yields and 90–97% ee. Experiments and DFT calculations supported the dual activation manner, in which the tridentateligand coordinated