Cioc Răzvan C, Smak Tom J, Crockatt Marc, van der Waal Jan C, Bruijnincx Pieter C A
Organic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University Universiteitsweg 99 3584 CG Utrecht The Netherlands
Department of Sustainable Process and Energy Systems, TNO Leeghwaterstraat 44 2628 CA Delft The Netherlands.
Green Chem. 2021 Jun 23;23(15):5503-5510. doi: 10.1039/d1gc01535d. eCollection 2021 Aug 2.
The furan Diels-Alder (DA) cycloaddition reaction has become an important tool in green chemistry, being central to the sustainable synthesis of many chemical building blocks. The restriction to electron-rich furans is a significant limitation of the scope of suitable dienes, in particular hampering the use of the furans most readily obtained from biomass, furfurals and their oxidized variants, furoic acids. Herein, it is shown that despite their electron-withdrawing substituents, 2-furoic acids and derivatives (esters, amides) are in fact reactive dienes in Diels-Alder couplings with maleimide dienophiles. The reactions benefit from a substantial rate-enhancement when water is used as solvent, and from activation of the 2-furoic acids by conversion to the corresponding carboxylate salts. This approach enables Diels-Alder reactions to be performed under very mild conditions, even with highly unreactive dienes such as 2,5-furandicarboxylic acid. The obtained DA adducts of furoic acids are shown to be versatile synthons in the conversion to various saturated and aromatic carbocyclic products.
呋喃的狄尔斯-阿尔德（DA）环加成反应已成为绿色化学中的一项重要工具，是许多化学结构单元可持续合成的核心。对富电子呋喃的限制是合适双烯范围的一个重大局限，尤其阻碍了最容易从生物质中获得的呋喃、糠醛及其氧化变体糠酸的应用。本文表明，尽管2-糠酸及其衍生物（酯、酰胺）具有吸电子取代基，但实际上它们在与马来酰亚胺亲双烯体的狄尔斯-阿尔德偶联反应中是活性双烯。当使用水作为溶剂时，反应受益于显著的速率增强，并且通过转化为相应的羧酸盐来活化2-糠酸。这种方法能够在非常温和的条件下进行狄尔斯-阿尔德反应，即使是与像2,5-呋喃二甲酸这样反应活性很低的双烯反应也可以。所得到的糠酸DA加合物在转化为各种饱和和芳香族碳环产物方面显示出是通用的合成子。
