两种常见受保护形式的胺(氨基甲酸酯和磺酰胺)在 Ni 催化的 Suzuki 反应中作为导向基团的能力已被用于开发用于交叉偶联未活化烷基亲电子试剂的催化不对称方法。在市售镍配合物和手性配体存在下,外消旋仲溴化物和氯化物在室温下以良好的 ee 立体收敛过程中形成 CC 键。旨在阐明与 Ni(氨基甲酸酯和磺酰胺的氧)结合的位点的结构对映选择性研究导致发现,砜也可用作外消旋烷基卤化物的不对称 Suzuki 交叉偶联的有用导向基团。据我们所知,这项研究提供了在金属催化的不对称 CC 键形成反应中使用磺酰胺或砜作为有效导向基团的第一个例子。一项机理研究表明,金属转移发生时保留了立体化学,并且由此产生的 Ni-C 键在催化循环的后续阶段不会发生均裂。
Nucleophilic 5-endo-trig cyclization of 2-(trifluoromethyl)allylic metal enolates and enamides: Synthesis of tetrahydrofurans and pyrrolidines bearing exo-difluoromethylene units
作者:Takeshi Fujita、Masahiro Hattori、Masaaki Matsuda、Ryutaro Morioka、Tanner C. Jankins、Masahiro Ikeda、Junji Ichikawa
DOI:10.1016/j.tet.2018.11.011
日期:2019.1
proceeded exclusively in each case to afford the corresponding five-membered heterocycles with both exo-difluoromethylene and exo-alkylidene units. On treatment with potassium hexamethyldisilazide (KHMDS) or lithium diisopropylamide (LDA), 2-(trifluoromethyl)allylic ketones or imines provided the corresponding tetrahydrofurans or pyrrolidines bearing a Z-alkylidene group with perfect or substantial stereoselectivity
A Simple and Effective Catalytic System for Epoxidation of Aliphatic Terminal Alkenes with Manganese(II) as the Catalyst
作者:Kam-Piu Ho、Wing-Leung Wong、Kin-Ming Lam、Cheuk-Piu Lai、Tak Hang Chan、Kwok-Yin Wong
DOI:10.1002/chem.200800759
日期:2008.9.8
A simple catalytic system that uses commercially available manganese(II) perchlorate as the catalyst and peracetic acid as the oxidant is found to be very effective in the epoxidation of aliphatic terminal alkenes with high product selectivity at ambient temperature. Many terminal alkenes are epoxidised efficiently on a gram scale in less than an hour to give excellent yields of isolated product (>90
Reaction of a variety of 1,2-epoxyalkanes with 2.5 equiv. of bulky metal amide—lithium 2,2,6,6-tetramethylpiperidide—affords the corresponding aldehydes exclusively in high yields; this is the first example of base-promotedisomerization of monosubstituted epoxides to aldehydes.
A simple and efficient method for epoxidation of terminal alkenes
作者:Christophe Copéret、Hans Adolfsson、K. Barry Sharpless
DOI:10.1039/a703542j
日期:——
The use of a catalytic amount of 3-cyanopyridine in the
methyltrioxorhenium catalysed epoxidation of terminal alkenes with aqueous
hydrogen peroxide speeds turnover, which results in the formation of many
functionalized epoxides in high yields.
of allyl t-butyl peroxide in cyclohexane and tetrahydrofuran shows that an important induced decomposition of the peroxide occurs by the addition of radicals derived from the solvent, to the peroxide double bond, followed by an intramolecular homolytic displacement of the t-butoxyl group. Such a reaction is a 2,3-epoxypropanation of the solvent in which the initiator is decomposed. The reaction is