Efficient Enantioselective Synthesis of Dihydropyrans Using a Chiral N,N′-Dioxide as Organocatalyst
摘要:
The bifunctional organocatalyst C3 N,N'-dioxide has been successfully applied to the asymmetric cascade Michael/hemiacetalization reaction of alpha-substituted cyano ketones and beta,gamma-unsaturated alpha-ketoesters for the synthesis of multifunctionalized chiral dihydropyrans. The corresponding products were obtained in excellent yields (up to 99%) with high to excellent enantioselectivities (up to 99% ee).
A catalytic asymmetric carbonyl-ene reaction of [small beta],[gamma]-unsaturated [small alpha]-ketoesters with 5-methyleneoxazolines was accomplished. The process was based on the utilization of a chiral N,N'-dioxide/MgII catalyst, providing the desired products with excellent...