Abstract
Cellulose nanofibers (CNFs) have recently attracted much attention as catalysts in various reactions. Organocatalysts have emerged as sustainable alternatives to metal-based catalysts in green organic synthesis, with concerted systems containing CNFs that are expected to provide next-generation catalysis. Herein, for the first time, we report that a representative organocatalyst comprising an unexpected combination of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized CNFs and proline shows significantly enhanced catalytic activity in an asymmetric Michael addition.
Highlights
In the last two decades, cellulose nanofibers (CNFs) have emerged as a promising state-of-the-art nanomaterial with a wide range of applications [1]
The investigation into TOCN/proline-concerted catalysis of the Michael addition started with the reaction of cyclohexanone (1a) with trans-β-nitrostyrene (2a), which has been widely employed as a benchmark reaction to assess the related catalytic systems [38,39] (Table 1)
Using TOCNs alone without proline did not promote the reaction, clearly suggesting that the cooperation of catalytically inactive TOCNs and low-activity proline was critical in enhancing the reaction efficiency of this Michael addition
Summary
In the last two decades, cellulose nanofibers (CNFs) have emerged as a promising state-of-the-art nanomaterial with a wide range of applications [1]. The regular assembly of dozens of molecular cellulose chains in one direction forms highly crystalline CNFs. CNFs are mainly derived from woody secondary cell walls and they possess an uncommon combination of features, such as high strength, high transparency, a large specific surface area, a well-defined nanoarchitecture, and a highly functionalized and chemically modifiable crystalline surface [2,3]. CNFs are mainly derived from woody secondary cell walls and they possess an uncommon combination of features, such as high strength, high transparency, a large specific surface area, a well-defined nanoarchitecture, and a highly functionalized and chemically modifiable crystalline surface [2,3] Taking advantage of these physicochemical properties, CNFs have been widely explored in polymer nanocomposite reinforcement [4] as high performance gas-separation films and purification membranes [5,6] and in the confection of electroactive paper [7,8]. In TOCNs, carboxylates are introduced onto native cellulose crystals at regular intervals and with high density, resulting in a core–shell structure, in which a glucose/glucuronic acid alternating copolymer covers native crystalline cellulose bundles
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