Vinylethers can be protonated to generate oxocarbenium ions that react with Me3SiCN to form cyanohydrin alkylethers. Reactions that form racemic products proceed efficiently upon conversion of the vinylether to an α-chloro ether prior to cyanide addition in a pathway that proceeds through Brønsted acid-mediated chloride ionization. Enantiomerically enriched products can be accessed by directly protonating
乙烯基醚可以质子化以生成氧代碳正离子,该离子与 Me 3 SiCN反应形成氰醇烷基醚。在通过布朗斯台德酸介导的氯离子电离进行的途径中,在加入氰化物之前将乙烯基醚转化为 α-氯醚后,形成外消旋产物的反应有效进行。可以通过用手性布朗斯台德酸直接质子化乙烯基醚以形成手性离子对来获得对映体富集的产品。Me 3 SiCN 作为亲核试剂,PhOH 在不对称双分子亲核加成到氧碳鎓离子的罕见例子中作为化学计量质子源。计算研究为催化剂和氧代碳正离子之间的相互作用提供了模型。
Enantioselective Claisen Rearrangements with a Hydrogen-Bond Donor Catalyst
作者:Christopher Uyeda、Eric N. Jacobsen
DOI:10.1021/ja803370x
日期:2008.7.1
m ion associated with the noncoordinating BArF counterion is shown to be an effective catalyst for the [3,3]-sigmatropic rearrangement of a variety of substitutedallylvinylethers. Highly enantioselective catalytic Claisenrearrangements of ester-substituted allylvinylethers are then documented using a new C2-symmetric guanidinium ion derivative.
A mixed ortho ester is prepared under mild conditions from an allyl alcohol and a ketene acetal in the presence of PdCl2(COD). The ortho ester thus formed is successively treated with a catalytic amount of PdCl2(PPh3)2 in refluxing p-xylene to afford a γ,δ-unsaturated ester in a high yield under neutral conditions.
Vinylation of Aryl Ether (Lignin β-O-4 Linkage) and Epoxides with Calcium Carbide through C−O Bond Cleavage
作者:Siew Ping Teong、Jenny Lim、Yugen Zhang
DOI:10.1002/cssc.201701153
日期:2017.8.24
carbide has been increasingly used as a sustainable, easy‐to‐handle, and low‐cost feedstock in organicsynthesis. Currently, methodologies of using calcium carbide as “solid acetylene” in synthesis are strictly limited to activation and reaction with X−H (X=C, N, O, S) bonds. Herein, a mild and transition‐metal‐free protocol was developed for the vinylation of epoxides and aryl ether linkage (β‐O‐4 lignin