The synthesis of α-stannyl-silanes and their use in the formation of alkenes
摘要:
alpha-Stannyl-silanes were prepared from aldehydes via alpha-hydroxy- and alpha-chloro-silanes. Stannyl-silane 5d was transmetallated using non-butylithium and the resultant alpha-lithio-silane condensed with aldehydes to yield alkenes.
imidazolium salts, γ-substituted allyl chlorides reacted with alkyl Grignard reagents to undergo substitution reactions in an SN2′-selective fashion, where the magnesium ate complexes [(N-heterocyclic carbene-MgR3)−(MgX)+] of imidazol-2-ylidenes or imidazol-4-ylidenes, generated in situ, were postulated as the active species. It was observed that the reactions with imidazol-4-ylidene catalysts were faster
在催化量的1,2-二取代或1,2,3-三取代的咪唑鎓盐的存在下,γ-取代的烯丙基氯与烷基格氏试剂反应,以S N 2'-选择性方式进行取代反应,其中假定将原位生成的咪唑-2-亚胺或咪唑-4-亚胺的镁盐配合物[(N-杂环卡宾-MgR 3)-(MgX)+ ]作为活性物质。观察到与咪唑-4-亚烷基催化剂的反应比与咪唑-2-亚烷基催化剂的反应更快。初步研究了使用手性咪唑盐的对映选择性催化。
Enantioselective Synthesis of Tertiary and Quaternary Stereogenic Centers: Copper/Phosphoramidite-Catalyzed Allylic Alkylation with Organolithium Reagents
作者:Martín Fañanás-Mastral、Manuel Pérez、Pieter H. Bos、Alena Rudolph、Syuzanna R. Harutyunyan、Ben L. Feringa
DOI:10.1002/anie.201107840
日期:2012.2.20
An efficient and highly enantioselectivecopper‐catalyzed allylic alkylation of disubstituted allyl halides with primary and secondary organolithium reagents using phosphoramidite ligands is reported. The use of trisubstituted allyl bromides allows, for the first time, the enantioselective synthesis of all‐carbon quaternary stereogenic centers with these reactive organometallic reagents.
dimethylphenylsilylmethylmagnesium chloride result in highly regioselective dehydrohalogenation. The reaction does not follow the conventional E2 elimination mechanism but includes beta-hydride elimination from the corresponding alkylcobalt intermediate. The interesting reaction mechanism of the cobalt-catalyzed dehydrohalogenation offered unique transformations that are otherwise difficult to attain.