在NMR动力学实验中,测量了酸催化环氧酯重排为[3.2.1]双环原酸酯的相对速率,这些原酸酯随后重排为取代的四氢呋喃的相对速率,以及在pH值为4.75时原酸酯水解的速率。这些原酸酯的形成容易性和稳定性与通常用作羧酸保护基的OBO型[2.2.2]双环原酸酯相比具有优势。用13 C NMR检测到的18 O-标记进行的研究表明,环氧酯重排优先通过6-exo环化发生,尽管当环氧化物的远端中心被双取代时,7-endo竞争。通过18 O标记显示原酸酯环醚重排仅通过五元二氧杂环鎓离子的中介发生。水解产物的结构还表明在水解过程中二氧戊酸根离子的中间性。讨论了海洋聚醚毒素的假设生物合成的意义。
A method for transition metal-free 1,2-carboboration of unactivated alkenes with bis(catecholato)diboron as the boron source in combination with alkyl halides as the alkyl component is introduced. The three-component reaction proceeds via a radical pathway on a broad range of unactivated alkenes, and the 1,2-carboboration products serve as valuable synthetic building blocks. Density functional theory
Oxidative Decarboxylation Enables Chemoselective, Racemization-Free Esterification: Coupling of α-Ketoacids and Alcohols Mediated by Hypervalent Iodine(III)
作者:Takeshi Nanjo、Natsuki Kato、Yoshiji Takemoto
DOI:10.1021/acs.orglett.8b02466
日期:2018.9.21
α-ketoacid could be converted into a reactive acylating agent by treatment with hypervalentiodine(III) species, and in so doing, we discovered a novel decarboxylative acylation of alcohols that affords a variety of esters in excellent yields. The esterification has been applied to a sterol bearing a free carboxylicacid and shows unique chemoselectivity. The procedure is racemization-free and operates
We herein described a practical and efficient protocol for hydrodifluoromethylation of unactivated alkenes using readily available difluoroacetic anhydride as a difluoromethyl source by merging photocatalysis and N-hydroxyphthalimide activation. This method features a wide substrate scope and excellent compatibility with various functional groups, as demonstrated by more than 50 examples, including
Deprotection of Homoallyl (<sup>h</sup>Allyl) Derivatives of Phenols, Alcohols, Acids, and Amines
作者:Bruce H. Lipshutz、Subir Ghorai、Wendy Wen Yi Leong
DOI:10.1021/jo900012z
日期:2009.4.3
The homoallyl moiety, (h)Allyl, is presented as a general protecting group for several functionalities. It can be chemoselectively removed via a sequential, one-pot cross-metathesis/elimination sequence.
[IrCl(cod)]2-catalyzed direct oxidative esterification of aldehydes with alcohols
[IrCl(cod)](2) catalyzed the oxidative esteritication of a variety of aldehydes with methanol as a solvent in combination with K2CO3 under mild conditions (rt, 12 h). The oxidative esterification reaction of aliphatic aldehydes also took place with olefinic alcohols as reagents in toluene under similar conditions. (c) 2007 Elsevier Ltd. All rights reserved.