One‐Pot Oxidative Passerini Reaction of Alcohols Using a Magnetically Recyclable TEMPO under Metal‐ and Halogen‐Free Conditions

Abstract

A novel domino oxidative Passerini threecomponent reaction (OP-3CR) has been successfully developed with either primary or secondary alcohols instead of their corresponding aldehydes or ketones by using a recyclable magnetic core-shell nanoparticle supported TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl) (MNST, 1). It has been shown that MNST is a highly effective and recyclable catalyst system in the metal-and halogen-free aerobic, oxidative, three-component Passerini reaction. To the best of our knowledge this method can be considered as the first example of a OP-3CR of alcohols under metal-and halogen-free reaction conditions. It should be also noted that there has been no precedent example of oxidative OP-3CR of secondary alcohols to their corresponding a-acyloxy carbox-A C H T U N G T R E N N U N G amides. The catalyst can be magnetically recycled and successfully reused in 14 subsequent reaction cycles with only slight decreases of its catalytic activity.

Facile TEMPO Immobilization onto Poly(acrylic acid)-Modified Magnetic Nanoparticles: Preparation and Property

“…This result also indicated that TEMPO was simply and conveniently attached to the particle surface Recently, Karimi and coworkers showed that TEMPO was linked to the surface of the aminopropyltriethoxysilanemodified magnetic nanoparticles through amide reduction using sodium cyanoborohydrides [29][30][31]. Another previously known example reported by Schätz et al [27] and Tucker-Schwartz and Garrell [28] is through "click" reaction using azide modified nanoparticles with TEMPO derivatives.…”

“…This approach combines a poly(acrylic acid) chain grafted from magnetic iron oxide nanoparticles and forms an ideal support material for 4-hydroxy-2,2 ,6,6 -tetramethylpiperidinyl-1-oxy (H-TEMPO). This novel method uses simple approaches and avoids potential harmful substances [27][28][29][30][31]; hence it is a facile and green approach to prepare iron oxide-based magnetic nanocomposite materials with efficient immobilization of TEMPO. The product was investigated as catalyst for alcohols/aldehydes or ketone transformation under both the Anelli [34] and Minisci [35] protocols.…”

“…Currently, different methods have been successfully used to immobilize TEMPO on magnetic nanoparticles, such as "click" chemistry [27,28], amine reduction [29][30][31], and encapsulation and polymer/ nanoparticle blends [32]. The design and synthesis of magnetic nanoparticles with polymer chains on its surface [33] for specific catalyst immobilization not only improves immobilization efficiency but also avoids the use of potential harmful substances such azides or cyanoborohydrides that are employed in previous works [27][28][29][30][31][32]. The polymer chains on the magnetic nanoparticles surface offer pendant functional groups for organocatalyst anchoring reaction.…”

Electrochemical TEMPO-Catalyzed Oxidative Ugi-Type Reaction

“…To circumvent this problem, the concept of generating the adequate carbonyl/imine electrophiles by means of the in situ oxidation of the corresponding alcohol/amine emerged. , As the first milestone in oxidative IMCRs, Zhu et al succeeded in performing an alcohol-based 3-component Passerini reaction by employing 2-iodoxybenzoic acid (IBX) as the stoichiometric oxidant (Scheme , eq (a)) . Whereas a catalytic version of this multicomponent process was later reported, , more attention was subsequently paid to oxidative 3-component Ugi–Joullié-type IMCRs, in which an amine or an aniline derivative serves as the imine/iminium precursor (Scheme , eq (b)). − …”

“…22 , 23 As the first milestone in oxidative IMCRs, Zhu et al succeeded in performing an alcohol-based 3-component Passerini reaction by employing 2-iodoxybenzoic acid (IBX) as the stoichiometric oxidant ( Scheme 1 , eq (a)). 24 Whereas a catalytic version of this multicomponent process was later reported, 25 , 26 more attention was subsequently paid to oxidative 3-component Ugi–Joullié-type IMCRs, in which an amine or an aniline derivative serves as the imine/iminium precursor ( Scheme 1 , eq (b)). 27 − 41 …”