Carbenes ring true: N‐Heterocycliccarbene (NHC) catalyzed reactions of α‐bromo‐α,β‐unsaturated aldehydes/α,β‐dibromoaldehydes with 1,3‐dinucleophilic reagents, such as 1,3‐dicarbonyl compounds, β‐enamino ketones, and β‐enamino esters through umpolung processes gave functionalized 3,4‐dihydropyranones and 3,4‐dihydropyridinones (see scheme). The availability of the starting materials, lack of external
a critical step affecting the efficiency of the NHC‐catalyzed γ‐butyrolactone formation via homoenolate addition to aryl aldehydes. A novel type of imidazolylidene catalyst with pendant alkoxy groups on the ortho‐N‐aryl groups is described. Catalyst of this sort facilitates the formation of the conjugated Breslow intermediate. Studies of the rate constants for homoenolate annulation affording γ‐butyrolactones
N-Heterocyclic Carbene-Catalyzed Reaction of Alkynyl Aldehydes with 1,3-Keto Esters or 1,3-Diketones
作者:Zhi-Qiang Zhu、Ji-Chang Xiao
DOI:10.1002/adsc.201000240
日期:2010.10.4
The N-heterocyclic carbene-catalyzed reaction of alkynyl aldehydes with 1,3-keto esters or 1,3-diketones has been studied. This protocol offers an entirely new, mild and atom-economical access to highly functionalized 3,4-dihydropyranones.
Synthesis of Functionalized Dihydrocoumarins by NHC-Catalyzed [3 + 3] Annulation of Enals with 2-Substituted Naphthoquinones
作者:Sayan Shee、Soumen Barik、Arghya Ghosh、Akkattu T. Biju
DOI:10.1021/acs.orglett.1c03059
日期:2021.10.15
The [3 + 3] annulation of α,β-unsaturated aldehydes with 2-substituted 1,4-naphthoquinones allowing the facile synthesis of functionalized dihydrocoumarins catalyzed by N-heterocyclic carbene (NHC) is reported. The initially formed NHC-homoenolates underwent an efficient Michael–isomerization–lactonization cascade to furnish the products. Preliminary studies on mechanism shed light on the homoenolate