N-Heterocyclic carbene-catalyzed enantioselective annulations: a dual activation strategy for a formal [4+2] addition for dihydrocoumarins
作者:Anna Lee、Karl A. Scheidt
DOI:10.1039/c4cc09590a
日期:——
A highly efficient asymmetric formal [4+2] annulation for the synthesis of dihydrocoumarins has been developed via an in situ activated NHC catalysis. Both electrophilic and nucleophilic species are generated in situ simultaneously whereby acyl imidazoles facilitated rapid formation of an NHC-enolate intermediate to afford the [4+2] dihydrocoumarin adducts.
Catalytic Asymmetric Synthesis of Chiral Dihydrobenzofurans through a Formal [4+1] Annulation Reaction of Sulfur Ylides and In Situ Generated<i>ortho</i>-Quinone Methides
作者:Qing-Qing Yang、Wen-Jing Xiao
DOI:10.1002/ejoc.201601186
日期:2017.1.10
The first example of a catalytic asymmetric formal [4+1] annulation reaction between sulfur ylides and in situ generated ortho-quinone methides (o-QMs) is reported in this work. A C2-symmetric chiral urea was identified to be the best H-bonding catalyst, affording a wide range of chiral 2,3-dihydrobenzofurans in high yields and moderate enantioselectivities [70–98 % yields, up to 89:11 e.r. (enantiomeric
在这项工作中报道了硫叶立德与原位生成的邻醌甲基化物 (o-QMs) 之间的催化不对称形式 [4+1] 环化反应的第一个例子。一种 C2 对称手性尿素被认为是最好的 H 键合催化剂,可提供范围广泛的手性 2,3-二氢苯并呋喃,收率高,对映选择性适中 [70–98% 收率,高达 89:11 er )]。