Supported gold nanoparticles as efficient and reusable heterogeneous catalyst for cycloisomerization reactions

Abstract

We report the utilization of a novel catalyst for cycloisomerizations. The novel catalyst system contains gold nanoparticles supported on Al-SBA15, which was prepared by the ball-milling process. We developed a greener methodology for synthesizing spiroindolines under heterogeneous conditions, using this novel class of supported gold nanoparticles in combination with microwave irradiation. The catalyst is highly reusable and selective. Cycloisomerization reaction yields ranged from good to excellent leading to the formation of two novel classes of six- and seven-membered heterocycles, which have been unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as the solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity

Leaching‐Free Supported Gold Nanoparticles Catalyzing Cycloisomerizations under Microflow Conditions

“…[9] To furtheri nvesti- gate the role of water in this matter, the reaction was performed with and without the addition of water in batch under microwavei rradiation( MW), which can be seen in Scheme 2. We found that the presence of water results in an accelerated formation of spiroindoline 2h.…”

“…[8] Recently,o ur group developed an ovelh eterogeneous gold catalyst, consisting of gold nanoparticles on an Al-SBA15 support,f or the cycloisomerization of Ugi-adducts. [9] Ther eactione nabled access to various spiroindolines and diazepino [1,2-b]indazoles.Am ajor advantage of the protocolw as the use of ethanol as as ustainable solvent in substitution for dichloromethane or other chlorinateds olvents, which are common for most gold-catalyzed reactions. [1] The scope of the reactionw as limitedw ith regard to the substitution pattern of the alkynes within the Ugi-adducts.M ores pecifically,a ni nternal alkyne bearing methyl, ethyl or para-methoxyphenyl groups,r esulted in prolonged reactiont imes under batch conditions, typicallyu sing catalyst loadings of 10 mol%a t8 08 8C.…”

Synthesis of 3‐Keto Pyridines from the Conjugated Allenone – Alkynylamine Oxidative Cyclization Catalyzed by Supported Au Nanoparticles

“…Supported Au(0) nanoparticles (Au NPs) have been proven as excellent catalysts in cycloisomerization transformations, where the activation of sp ‐carbon π bonds (alkynes or allenes) on the low coordinated electrophilic Au atoms at the corners or edges of nanoparticles triggers intramolecular nucleophilic attack by carbon nucleophiles (Scheme ) . Thus, simple 1,6‐enynes, N ‐((1 H ‐indol‐3‐yl)methyl)propiolamides ( N ‐1,6‐enynes), aryl propargyl ethers, or ω‐alkynylfurans undergo cyclization in the presence of catalytic amounts of supported Au nanoparticles. In addition, the activation of an alkyne or allene by Au NPs may trigger inter or intramolecular nucleophilic attack by nitrogen, oxygen, or other nucleophiles.…”

Metal‐Free Dearomatization: Direct Access to Spiroindol(en)ines in Batch and Continuous‐Flow

“…[14] In 1997, Trost described the phosphine-catalyzed a-umpolung Michael reactiono fa lkyl esters with sulfonyla mine or phthalimide to achieve a-aminoc arbonyl compounds (Scheme 1d). [15] The reactionp roceeds through severali ntermediates, of which intermediate II could be trapped with different nucleophiles.With our enduring interesti ns piroindol(en)ines, [16] we planned to trap the intermediate II through an intramolecular nucleophilic attack of the C-3 position of the indole (Scheme 1e).Scheme1.Background on spiroindolenines framework.[a] P.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.…”