Regio- and stereoretentive synthesis of branched, linear (E)- and (Z)-allyl fluorides from allyl carbonates under Ir-catalysis
作者:Elena Benedetto、Matthew Tredwell、Charlotte Hollingworth、Tanatorn Khotavivattana、John M. Brown、Véronique Gouverneur
DOI:10.1039/c2sc21789a
日期:——
This paper describes a new catalytic method for the regio- and stereocontrolled fluorination of allylic carbonates. This transformation uses TBAF·4tBuOH as the fluoride source and [Ir(COD)Cl]2 as the catalyst; the most commonly used [Ir(COD)Cl]2/phosphoramidite system is ineffective. Synthetically, this reaction is characterized by a high degree of structural conservation in going from substrates to the products. The fluorination of (E)-allylic carbonates leading to linear (E)-allylic fluorides (l : b > 20 : 1, E : Z > 20 : 1) is unprecedented and a unique feature of fluoride as the nucleophile. The first examples of transition metal catalyzed fluorination affording (Z)-allyl fluorides (Z : E ratio >20 : 1) are disclosed along with the successful fluorination of branched, linear (E)- and (Z)-allyl carbonates with [18F] fluoride in the presence of [Ir(COD)Cl]2. 18O-Labeling of the reactant reveals internal return during the allylic ionization step, and pathways for effective intra- and intermolecular isotope exchange.
本文介绍了一种新的催化方法,用于烯丙基碳酸酯的区域和立体控制氟化反应。这种转化使用 TBAF-4tBuOH 作为氟源,[Ir(COD)Cl]2 作为催化剂;最常用的 [Ir(COD)Cl]2/ 磷酰胺体系无效。从合成角度看,该反应的特点是从底物到产物的过程中结构高度保持不变。(E)-烯丙基碳酸酯的氟化反应可生成线性(E)-烯丙基氟化物(l : b > 20 : 1,E : Z > 20 : 1),这是前所未有的,也是氟化物作为亲核体的一个独特特征。首次公开了过渡金属催化氟化反应生成 (Z)- 烯丙基氟化物(Z : E 比 >20 : 1)的实例,以及在 [Ir(COD)Cl]2 存在下用 [18F] 氟化氢成功氟化支链、线型 (E)- 和 (Z)- 烯丙基碳酸盐的实例。反应物的 18O 标记揭示了烯丙基离子化步骤中的内部返回,以及分子内和分子间有效同位素交换的途径。