从容易获得的α,β-环氧酮制备了一系列迄今未知的3,4-环氧-1,1-二氟丁烯,发现这些化合物发生了区域选择性S N 2'反应,并在高度阳性时与硬RLi亲核试剂发生反应。与仅具有低区域选择性的相应非氟化乙烯基氧杂环戊烷的情况形成鲜明对比的是,带电末端具有氟的sp 2碳原子形成鲜明的对比。HMPA的加入大大改善了产物的烯属立体选择性。理论计算被用来定性地探索这些反应中选择性的性质。
Asymmetric Cascade Catalysis with Chiral Polyoxometalate-Based Frameworks: Sequential Direct Aldol and Epoxidation Reactions
作者:Qiuxia Han、Wenwen Li、Shugai Wang、Jiachen He、Wei Du、Mingxue Li
DOI:10.1002/cctc.201700160
日期:2017.5.23
applied in the conversion of aldehyde with ketone into value‐added chiral epoxy ketones in a one‐pot procedure. The chiral pyrrolidine organocatalysts interact with the carbonyl group of ketones throughout the reaction, which is beneficial for achieving compatibility between the reaction intermediates and synergy of the multiple catalytic cycles, thus driving the directaldol/epoxidation cascade reaction
A Highly Efficient Solvent-Free Asymmetric Direct Aldol Reaction Organocatalyzed by Recoverable (<i>S</i>)-Binam-<scp>l</scp>-Prolinamides. ESI-MS Evidence of the Enamine−Iminium Formation
作者:Gabriela Guillena、Maria del Carmen Hita、Carmen Nájera、Santiago F. Viózquez
DOI:10.1021/jo800773q
日期:2008.8.1
equiv but also the reaction time to give the aldol products with regio-, diastereo-, and enantioselectivities comparable to those in organic or aqueous solvents. Generally anti-isomers are mainly obtained with enantioselectivities up to 97%. The reaction can be carried out under these conditions also using aldehydes as nucleophiles, yielding after in situ reduction of the aldol products the corresponding
Asymmetric Epoxidation of Enones by Peptide-Based Catalyst: A Strategy Inverting Juliá–Colonna Stereoselectivity
作者:Kazuaki Kudo、Kengo Akagawa、Tomoaki Hirata
DOI:10.1055/s-0035-1560597
日期:——
A resin-supported peptide catalyst with an N-terminal primary amino group was developed for asymmetric epoxidation of enones through iminium activation. The peptide has N-terminal l -3-(1-pyrenyl)alanine, a non-natural amino acid with a bulky side chain, which is connected to l -proline and then to 310-helical ( l -Leu- l -Leu-Aib)2 (Aib: 2-aminoisobutyric acid). This peptide successfully catalyzed
开发了一种带有 N 端伯氨基的树脂负载肽催化剂,用于通过亚胺活化对烯酮进行不对称环氧化。该肽具有 N 端 l -3-(1-芘基)丙氨酸,一种具有庞大侧链的非天然氨基酸,连接到 l -脯氨酸,然后连接到 310-螺旋 ( l -Leu- l -Leu -Aib)2(Aib:2-氨基异丁酸)。该肽成功地催化了芳基上带有吸电子基团的 β-芳基取代的烯酮的不对称环氧化反应。本肽催化剂的特点是对映选择性的意义与Julia-Colonna反应相反,低聚-l-Leu催化烯酮环氧化,而两种肽催化剂均由l-氨基酸组成。
α-Chloroacetone as a donor in the BINAM-l-prolinamide organocatalyzed aldol reaction: application to the enantioselective synthesis of α,β-epoxy ketones
作者:Gabriela Guillena、María del Carmen Hita、Carmen Nájera
DOI:10.1016/j.tetasy.2007.05.029
日期:2007.6
Recoverable (S-a)-BINAM-L-prolinamide in combination with benzoic acid catalyzed the direct aldol reaction between alpha-chloroacetone and several aldehydes in different solvents, including water. It is possible to obtain mainly one of the isomers with good regio-, diastero-, and enantioselectivity by choosing the appropriate solvent and reaction conditions. Thus, alpha-chloroacetone mainly gives the anti-aldol isomer in DMF/H2O with up to 97% ee. The crude a-chloro-p-hydroxy ketones obtained are transformed stereo specifically into the corresponding enantioenriched trans-alpha,beta-epoxy ketones derivatives with up to 97% ee through an S(N)2 displacement reaction by treatment with Et3N. (c) 2007 Elsevier Ltd. All rights reserved.