近年来,芳基卤化物和苄基卤化物与 CO2 的羧化取得了重大进展,成为使用化学计量量明确的金属物质的方便替代品。然而,这些过程中的大多数都需要使用自燃和空气敏感试剂,目前的方法主要限于有机卤化物。因此,非常希望发现一种温和的、操作简单的替代羧化反应,该羧化反应在广泛的底物范围内使用容易获得的偶联伙伴发生。在此,我们报告了一种新的协议,该协议涉及 CO2 协同活化的开发和惰性 C(sp(2))-O 和 C(sp(3))-O 键的相当具有挑战性的活化,这些键源自简单且廉价的酒精,这是该领域以前未被认识到的机会。这种前所未有的羧化事件的特点是其简单、温和的反应条件、显着的选择性模式以及使用对空气、水分不敏感且易于处理的镍预催化剂的优异化学选择性曲线。我们的结果使我们的方法成为一种强大的替代方案,实用性和新颖性,可以替代常用的有机卤化物作为羧化方案中的对应物。此外,这项研究首次表明,无痕导向基团允许在没有扩展
Iron(III)-catalyzed direct synthesis of diphenylmethyl esters from 2-diphenylmethoxypyridine
作者:Van Hieu Tran、Minh Thanh La、Hee-Kwon Kim
DOI:10.1080/00397911.2019.1625063
日期:2019.9.17
has been developed for the synthesis of diphenylmethyl (DPM) esters from 2-diphenylmethoxypyridine. Various carboxylic acids readily reacted with 2-diphenylmethoxypyridine in the presence of FeCl3 as a catalyst to provide the desired DPM esters with high yields. The procedure is facile and enables effective synthesis of a variety of esters for the protection of carboxylic acids. Graphical Abstract
Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles
作者:Nivedita S. Mahajani、Rowan I. L. Meador、Tomas J. Smith、Sarah E. Canarelli、Arijit A. Adhikari、Jigisha P. Shah、Christopher M. Russo、Daniel R. Wallach、Kyle T. Howard、Alexandra M. Millimaci、John D. Chisholm
DOI:10.1021/acs.joc.9b00745
日期:2019.6.21
Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Brønsted acids. With heating, these reactions have been extended to benzyl esters without electron-donating groups. These inexpensive
Diphenylmethyl trichloroacetimidate is a useful reagent for the protection of carboxylic acids as their corresponding diphenylmethyl esters. These esterifications proceed rapidly without the need for an added catalyst or promoter. A variety of carboxylic acid substrates undergo esterification in excellent yields with the trichloroacetimidate reagent, including substrates possessing acid- or base-sensitive functionality. Protection of a carboxylic acid with a highly enolizable alpha-stereocenter using diphenylmethyl imidate was also accomplished without racemization.