RESUMO
Herein, an efficient method for asymmetric α-amination of 2-benzofuranones with N-heterocyclic carbene (NHC) catalysis is reported. The process is based on non-covalent interaction of NHC with substrate, facilitating the formation of a chiral ion-pair that encompasses enolate and azolium salt. The activated enolate adds to an electrophilic amine source with sufficient facial control to furnish an enantioenriched product having an amine substituted quaternary stereocenter. The process displays a broad substrate scope. A preparative scale synthesis has been achieved. Preliminary mechanistic investigations based on experimental and DFT studies suggest a reaction pathway that involves non-covalent substrate/NHC interactions and essentially implicate the role of π-π interaction in diastereomeric transition states for stereo-chemical discrimination.
RESUMO
Enantioenriched acyclic α-substituted ß-hydroxy amides are valuable compounds in chemical, material and medicinal sciences, but their enantioselective synthesis remains challenging. A catalytic kinetic resolution (KR) of such amides with selectivity factor(s) up to >200 is developed via enantioselective acylation of primary alcohol with N-heterocyclic carbene. An enhanced selectivity for the catalytic KR process is realized using cyclic tertiary amine as base additive. Diastereomeric transition state models for the process are proposed to rationalize the origin of enantioselectivity.
RESUMO
Herein, successful utilization of non-covalent N-heterocyclic carbene (NHC) catalysis toward asymmetric aminative dearomatization of naphthols is presented. The NHC-catalyzed process offers enantioselective synthesis of cyclic enones possessing a nitrogen-containing α-quaternary stereocenter. The reaction applies to various functionalized substrates including acid-labile groups and is shown to be scalable. Substrate activation via an O-H···NHC hydrogen-bonding interaction is suggested based on the results obtained in mechanistic studies.