Synthesis of Enantiopure 2-C-Glycosyl-3-nitrochromenes
摘要:
A novel methodology has been developed to obtain enantiopure 2-C-glycosyl-3-nitrochromenes. First, (Z)-1-bromo-1-nitroalkenes were prepared from the corresponding sugar aldehydes through a sodium iodide-catalyzed Henry reaction with bromonitromethane followed by elimination of the resulting 1-bromo-1-nitroalkan-2-ols. In the next step, reaction of the sugar-derived (Z)-1-bromo-1-nitroalkenes with o-hydroxybenzaldehydes afforded enantiopure (2S,3S,4S)-3-bromo-3,4-dihydro-4-hydroxy-3-nitro-2H-1-benzopyrans, which, upon SmI2-promoted beta-elimination, yielded chiral enantiopure 2-C-glycosyl-3-nitrochromenes.
Heterogeneous enantioselective synthesis of chromans via the oxa-Michael–Michael cascade reaction synergically catalyzed by grafted chiral bases and inherent hydroxyls on mesoporous silica surface
作者:Shanshan Wang、Jing He、Zhe An
DOI:10.1039/c7cc03556j
日期:——
A heterogeneous enantioselective oxa-Michael–Michael reaction for the synthesis of chromans has been developed on a heterogeneous acid–base synergic catalyst with inherent silica as acidic sites and immobilized chiral amines as basic sites. Final products were afforded in selectivity of up to 98% and ee of 97% from 2-nitrovinyl phenol and 3-methyl-2-butenal. The heterogeneous synergistic catalytic
Enantioselective Synthesis of 2-Aryl-3-nitro-2H-chromenes Catalyzed by a Bifunctional Thiourea
作者:Peter Schreiner、Zhiguo Zhang、Gergely Jakab
DOI:10.1055/s-0030-1259956
日期:2011.6
A bifunctional thiourea-catalyzed tandem approach of oxa-Michael―aza-Henry―desulfonamidation was used to synthesize chiral 2-aryl-3-nitro-2H-chromenes. This method provides direct access to the corresponding products in moderate to good yields and enantioselectivities.
Asymmetric Direct Michael Reactions of Cyclohexanone with Aromatic Nitroolefins in Water Catalyzed by Novel Axially Unfixed Biaryl-Based Bifunctional Organocatalysts
new family of axiallyunfixedbiaryl-basedwater-compatible bifuctional organocatalysts were designed and synthesized for the asymmetric direct Michael reaction of cyclohexanone with various nitroolefins in water. One of the organocatalysts incorporates pyrrolidine and arylsulfonamide motifs as active organocatalytic sites, and axiallyunfixed biaryl as a skeleton; with this organocatalyst, the direct
设计并合成了一类新的轴向未固定联芳基水相容双功能有机催化剂,用于环己酮与水中各种硝基烯烃的不对称直接迈克尔反应。其中一种有机催化剂包含吡咯烷和芳基磺酰胺基序作为活性有机催化位点,以及轴向未固定的联芳基作为骨架;使用这种有机催化剂,直接迈克尔反应很容易进行,以高产率(高达 99% 的产率)提供所需的迈克尔加合物,并具有高水平的立体控制(高达 >99:1 dr 和 94% ee)。
Augmentation of Enantioselectivity by Spatial Tuning of Aminocatalyst: Synthesis of 2-Alkyl/aryl-3-nitro-2<i>H</i>-chromenes by Tandem Oxa-Michael–Henry Reaction
作者:Rahul Mohanta、Ghanashyam Bez
DOI:10.1021/acs.joc.9b03366
日期:2020.4.3
The asymmetric oxa-Michael addition of salicylaldehyde to conjugatednitroalkenes often suffers from poor reactivity and selectivity and a long reaction time. Because of the formation of an iminium ion with aminocatalyst, the nucleophilicity of the phenolic hydroxy group in salicylaldehyde reduces further to make the oxa-Michael reaction reversible. Here, we report a structurally simple and easily
Synthesis of substituted chiral chromans via organocatalytic kinetic resolution of racemic 3-nitro-2-aryl-2H-chromenes with ketones catalyzed by pyrrolidinyl-camphor-derived organocatalysts
作者:Dhananjay R. Magar、Kwunmin Chen
DOI:10.1016/j.tet.2012.05.019
日期:2012.7
pyrrolidinyl-camphor derivative 2b as a bifunctionalorganocatalyst under neat conditions in the presence of AcOH at 0 °C. In general, the organocatalyticasymmetricMichaeladdition of ketones proceeded smoothly to give the functionalized Michael adducts (3a–n) with good-to-high diastereo- and enantioselectivities (up to 92:8 dr, 93% ee, and 47% yield). The less reactive chromenes (S)-1a–h, k, l and (R)-1i–j were