Regioselectivity of Birch Reductive Alkylation of Biaryls
作者:Raphaël Lebeuf、Frédéric Robert、Yannick Landais
DOI:10.1021/ol051377i
日期:2005.10.1
regioselectivity of the Birchreductive alkylation of polysubstituted biaryls has been investigated. Results indicate that regioselectivity is affected by the electronic nature of substituents on both aromatic rings. The electron-rich 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and aniline are not dearomatized under these conditions. Biaryls possessing a phenol moiety are
5-dimethoxyphenyl moiety and a phenol ring may, however, be reduced and alkylated provided the acidic phenolic proton is removed prior to the treatment with Li in NH3. Similarly, biaryls possessing a o-sulfonamide group are reduced regioselectively and alkylated with α-chloroacetonitrile or N-tosylaziridine to provide the corresponding dienes in reasonable to good yields. A survey of the alkylating agents was also
通过改变芳环上取代基的性质,进行了联芳基的桦树还原性烷基化。我们的研究集中在富含电子的取代基(例如OMe,OH和NR 2基团)上,因为它们存在于目标生物碱的骨架上。区域选择性受两个环上这些取代基的电子性质的强烈影响。3,5-二甲氧基苯基部分被选择性还原然后烷基化,而苯酚和苯胺在这些条件下不发生反应。但是,只要在用Li在NH 3中处理之前除去酸性酚质子,就可以还原同时具有3,5-二甲氧基苯基部分和酚环的联芳基并烷基化。类似地,联芳基化合物具有一个Ô-磺酰胺基区域选择性地还原,并用α-氯乙腈或N-甲苯磺酰基氮丙啶烷基化,以合理至良好的产率提供相应的二烯。还对烷基化剂进行了调查,结果表明可以在苄基位置引入各种官能团,包括酯,伯和叔酰胺,腈,环氧化物和乙缩醛,以及未官能化的空间位阻t- Bu基和环丙基取代基。引入后者的表示两个A S Ñ 2和SET机构可以在所述烷基化步骤进行。
Base-Catalyzed Intramolecular Hydroamination of Cyclohexa-2,5-dienes: Insights into the Mechanism through DFT Calculations and Application to the Total Synthesis of<i>epi</i>-Elwesine
The base‐catalyzed intramolecular hydroamination of 1‐ethylaminocyclohexa‐2,5‐dienes is described. The transformation proceeds through isomerization of the cyclohexa‐1,4‐dienyl fragment into the corresponding conjugated 1,3‐diene prior to the hydroamination step. Attaching a chiral glycinol ether auxiliary on the amino group allows the protonation to occur with complete diastereocontrol. The resulting
Palladium-Catalyzed Enantioselective Desymmetrizing Aza-Wacker Reaction: Development and Application to the Total Synthesis of (−)-Mesembrane and (+)-Crinane
作者:Xu Bao、Qian Wang、Jieping Zhu
DOI:10.1002/anie.201712521
日期:2018.2.12
good yields with excellent enantioselectivities. A cooperative effect between the phosphoric acid and the pyrox ligand ensured efficient transformation. This reaction was tailor‐made for Amaryllidaceae and Sceletium alkaloids as illustrated by its application in the development of the concise and divergenttotalsynthesis of (−)‐mesembrane and (+)‐crinane.