Two-step synthesis of (.gamma.,.gamma.-difluoroallyl)carbonyl compounds via addition of 1,1,2-trichloro-2,2-difluoroethyl radical to silyl enol ethers followed by reductive dechlorination
摘要:
Ru(II)- or Cu(I)-induced radical reaction of CF2ClCCl2. radical (2), regioselectively derived from CF2ClCCl3, to trimethylsilyl enol ethers and a ketene silyl acetal yields (beta,beta,gamma-trichloro-gamma,gamma-difluoropropyl)carbonyl compounds 5 as the intermediates. Spontaneous dehydrochlorination affords [beta-chloro-beta-(chlorodifluoromethyl)vinyl]carbonyl compounds 4. Reductive dechlorination of 4 with zinc gave gamma,gamma-difluoroallyl ketones 7a-e and an ester 7f. In some cases, Ni(0)-catalyzed reduction with zinc is superior than the simple hydrodechlorination.
Manifestation of Polar Reaction Pathways of 2,3-Dichloro-5,6-dicyano-<i>p</i>-benzoquinone
作者:Xingwei Guo、Herbert Mayr
DOI:10.1021/ja405890d
日期:2013.8.21
Reactions of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) with silyl enol ethers, silyl ketene acetals, allylsilanes, enamino esters, and diazomethanes have been studied in CH3CN and CH2Cl2 solutions. The second-order rate constants for C attack at DDQ (log k(C)) correlate linearly with the nucleophile-specific parameters N and s(N) and are 2-5 orders of magnitude larger than expected for SET processes
已在 CH3CN 和 CH2Cl2 溶液中研究了 2,3-二氯-5,6-二氰基-对苯醌 (DDQ) 与甲硅烷基烯醇醚、甲硅烷基乙烯酮缩醛、烯丙基硅烷、烯氨基酯和重氮甲烷的反应。DDQ 处 C 攻击的二阶速率常数 (log k(C)) 与亲核试剂特定参数 N 和 s(N) 线性相关,并且比 SET 过程的预期大 2-5 个数量级,这强烈支持CC键形成的极性机制。O 攻击的二阶速率常数与用于确定速率的单电子转移 (SET) 的计算速率常数非常吻合。由于自由基时钟实验排除了外球电子转移,因此建议 O 攻击采用内球电子转移机制。
Triethylborane Induced Perfluoroalkylation of Silyl Enol Ethers and Ketene Silyl Acetals with Perfluoroalkyl Iodides
perfluoroalkyl iodides with silyl enol ethers mediated by Et3B in the presence of base such as 2,6-dimethylpyridine provides mixtures of perfluoroalkylated trialkylsilyl enol ethers and α-perfluoroalkylated ketones. The yield and distribution of the products heavily depend on the nature of base employed. Treatment of a reaction mixture consisting of perfluoroalkylated silyl enol ether and α-perfluoroalkylated
electrophilic activation of aromatic carbonyl substrates, by utilizing donor–acceptor interactions between an electron‐deficient macrocyclic boronic ester host ([2+2]BTH‐F) and an aromatic carbonyl guest substrate, was realized. In the presence of a catalytic amount of [2+2]BTH‐F, dramatic acceleration of the nucleophilic addition of a ketene silyl acetal towards either electron‐rich aromatic aldehydes or ketones
Catalytic Enantioselective Mannich-type Reactions of Ketoimines
作者:Yutaka Suto、Motomu Kanai、Masakatsu Shibasaki
DOI:10.1021/ja068226a
日期:2007.1.1
(10 mol %) and (EtO)2Si(OAc)2 as the trapping reagent (1 equiv) of the intermediate copper amide (generated via the addition of a copper enolate to the imine). The trapping reagent significantly facilitated the catalyst turnover. Excellent enantioselectivity was produced from a range of aromatic ketoimines, including heteroaromatic and ethyl-substituted ketoimines. The optimized conditions for aliphatic
Asymmetric Total Synthesis of Pre-schisanartanin C
作者:Yan-Long Jiang、Hai-Xin Yu、Yong Li、Pei Qu、Yi-Xin Han、Jia-Hua Chen、Zhen Yang
DOI:10.1021/jacs.9b11872
日期:2020.1.8
Pre-schisanartanin C belongs to the family of Schisandra nortriterpenoids with potent antihepatitis, antitumor, and anti-HIV activities. This paper presents the enantioselective total synthesis of pre-schisanartanin C (1). An important step in the total synthesis of 1 is gold-catalyzed intramolecular cyclopropanation of an 1,8-enyne substrates bearing a secondary ester group at the propargylic position
五味子素前体 C 属于五味子降三萜类化合物家族,具有有效的抗肝炎、抗肿瘤和抗 HIV 活性。本文介绍了前五味子素 C (1) 的对映选择性全合成。1 的全合成中的一个重要步骤是金催化的分子内环丙烷化,在炔丙基位置带有仲酯基的 1,8-烯炔底物制备双环 [6.1.0] 壬烷核。其他亮点包括 i) 不对称 Diels-Alder 反应以安装 1 的初始 C5 立体中心,以及 ii) 顺序 Pd 催化的 Stille 偶联、区域和立体选择性 Sharpless 不对称二羟基化,以及随后的分子内内酯化以构建1的侧链