Hindered organoboron groups in organic chemistry. 25. The condensation of aliphatic aldehydes with dimesitylboryl stabilised carbanions to give alkenes.
作者:Andrew Pelter、Keith Smith、Said M.A. Elgendy
DOI:10.1016/s0040-4020(01)87983-7
日期:1993.8
In the presence of protic acids the condensation of aliphatic aldehydes with dimesitylboryl stabilised carbanions results in alkenes. In the presence of strong acids such as HCl or CF3SO3H, the products contain > 90% of E-alkenes in all cases tried. When acetic acid is used, then Z-alkenes may result predominantly, particularly in the cases of RsCHO and RtCHO. HX HCI, CF3SO3H gives E - alkenes in
在质子酸的存在下,脂族醛与二聚三苯甲基稳定的碳负离子的缩合会生成烯烃。在强酸(例如HCl或CF 3 SO 3 H)的存在下,在所有尝试的情况下,产品均含有> 90%的E-烯烃。当使用乙酸时,则可能主要产生Z-烯烃,特别是在R s CHO和R t CHO的情况下。在所有情况下,HXHCl,CF 3 SO 3 H均会生成E-烯烃。HXCH 3 CO 2 H,使得主要ž -烯烃当Rř秒,R叔。
Improvements and Applications of the Transition Metal-Free Asymmetric Allylic Alkylation using Grignard Reagents and Magnesium Alanates
作者:David Grassi、Alexandre Alexakis
DOI:10.1002/adsc.201500495
日期:2015.10.12
Two new N-heterocyclic carbene (NHC) ligands have been synthesized and employed in the transition metal-free asymmetric allylic alkylation (AAA) mediated by Grignardreagents and magnesium alanates. The employment of these ligands showed high yields and improved regio- and enantioselectivity in the formation of tertiary and quaternary stereocenters. Moreover, the low catalyst loading (up to 0.3 mol%)
The Cu‐free asymmetric allylic alkylation, catalysed by NHC, with Grignardreagents is reported on allyl bromide derivatives with good results. The enantioselectivity was quite homogeneous (around 85 % ee) on large and various substrates, regardless of the nature of the Grignardreagent. The formation of stereogenic quaternary centres was highly regioselective for both aliphatic and aromatic derivatives
Copper-Free Asymmetric Allylic Alkylation with Grignard Reagents
作者:Olivier Jackowski、Alexandre Alexakis
DOI:10.1002/anie.201000577
日期:2010.4.26
Open wide and say AAA: The copper‐free asymmetric allylicalkylation reaction of Grignardreagents, catalyzed by N‐heterocyclic carbenes, is reported for allyl bromide derivatives. This reaction offers good enantioselectivity and good to excellent γ regioselectivity, particularly for the formation of quaternary chiral centers (see scheme; Mes=mesityl).
张开嘴说AAA:据报道,N-杂环卡宾催化了格氏试剂的无铜不对称烯丙基烷基化反应,是烯丙基溴衍生物的反应。该反应提供了良好的对映选择性和良好的至优异的γ区域选择性,特别是对于形成四元手性中心(参见方案; Mes =甲磺酰基)。
NiH‐Catalyzed Remote Asymmetric Hydroalkylation of Alkenes with Racemic α‐Bromo Amides
作者:Fang Zhou、Yao Zhang、Xianfeng Xu、Shaolin Zhu
DOI:10.1002/anie.201813222
日期:2019.2.4
Reported here is a terminal‐selective, remote asymmetric hydroalkylation of olefins with racemic α‐bromo amides. The reaction proceeds by NiH‐catalyzed alkene isomerization and subsequent alkylation reaction, and can enantioconvergently introduce an unsymmetrical secondary alkyl group from a racemic α‐bromo amide onto a terminalC(sp3)−H position along the hydrocarbon chain of the alkene. This mild process