α,β-Unsaturated Acyl Azoliums from N-Heterocyclic Carbene Catalyzed Reactions: Observation and Mechanistic Investigation
作者:Jessada Mahatthananchai、Pinguan Zheng、Jeffrey W. Bode
DOI:10.1002/anie.201005352
日期:2011.2.11
Caught in the act: Acyl azoliums have long been thought to be key reactive intermediates in N‐heterocycliccarbene catalysis, but they have never been observed under catalytic conditions. Now, this has been successfully achieved by the characterization of α,β‐unsaturated acyl azoliums (see scheme) using different spectroscopic techniques. Kinetic studies revealed the origin of their unexpected chemoselectivity
Asymmetric Synthesis of 4-Aryl-3,4-dihydrocoumarins by <i>N</i>-Heterocyclic Carbene Catalyzed Annulation of Phenols with Enals
作者:Guo-Tai Li、Zhi-Ke Li、Qing Gu、Shu-Li You
DOI:10.1021/acs.orglett.7b00088
日期:2017.3.17
enantioselective synthesis of 4-aryl-3,4-dihydrocoumarins was realized through direct annulation of phenols with enalscatalyzed by dihydroisoquinoline-type NHC (DHIQ-NHC), an N-heterocycliccarbene derived from l-phenylalanine. The catalytic reaction proceeds with a wide scope of electron-rich phenols and enals providing structurally diverse 4-aryl-3,4-dihydrocoumarins in good to excellent yields