Development of Aerobic Copper-Catalyzed Alcohol Oxidations for Synthesis and Lignin Valorization

Eemil Salonen

Research output: ThesisDoctoral ThesisMonograph

Abstract

The conversion of alcohols to carbonyls is one of the core transformations in organic chemistry. Due to its widespread utilization in laboratories and chemical industry, and tightening environmental regulations, continuous development of this field is an essential goal. This thesis focuses on aerobic copper-based catalysis designed for selective alcohol oxidations useful in synthesis and for oxidative conversion of wood-based lignin polymer to deliver value-added biochemicals. The first part of this thesis deals with the advent and advances of biomimetic Cu-catalyst systems devised for aerobic alcohol oxidations. Following the literature overview, the aim was to study chemoselectivity with challenging diol substrates as well as to improve the catalytic efficiency over different classes of primary alcohols. The second part of the thesis contributes to the synthesis of the C8–C19 fragment of calyculin C, a highly bioactive natural product. While the optimal Cu/TEMPO-catalyzed alcohol oxidation was applied in the synthesis, the specific focus was on the construction of the challenging stereotetrad unit. The correct relative stereochemistry was evidently assigned but the determination of the absolute configuration requires further work for which suggestions were provided. The third part forms the ultimate focus of this thesis. The project concerned the valorization of lignin fraction, which faces major challenges compared to the carbohydrate portion (hemicellulose and cellulose) of wood biomass, but serves as an ideal resource for the production of renewable aromatic chemicals. The initial idea to activate the lignin depolymerization via alcohol oxidation eventually led to the development of two types of Cu/TEMPO-based catalyst systems. In the first method, careful mechanistic studies showed that unstable aldehydes arising from chemoselective primary alcohol oxidation served as the key intermediates during the copper-mediated cascade delivering simple aromatic aldehydes from dimeric β-O-4 lignin model compounds. The quest to successfully apply the Cu-based oxidation to lignin conversion was accomplished with an improved protocol, where the reaction medium served as one of the key adjustments. Oxidative depolymerization of Finnish birch lignin delivered total four phenolic aldehydes and acids as the explicit major monomeric products to which three main reaction pathways were proposed based on reaction profiling and mechanistic studies with several model compounds. Finally, aiming to address the further potential of the oxidative methodology for early-stage catalytic conversion of lignin, the thesis culminates to studies using Finnish birch and pine sawdust as direct feedstocks. In this one-pot strategy, the major aromatic monomers were obtained in higher overall yield compared to the two-step lignin isolation-oxidation process.
Translated title of the contributionAerobisten kuparikatalysoitujen alkoholien hapetukset synteesiin ja ligniinin valorisaatioon
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Koskinen, Ari, Supervising Professor
  • Koskinen, Ari, Thesis Advisor
  • Joensuu, Pekka, Thesis Advisor
Publisher
Print ISBNs978-952-64-0115-7
Electronic ISBNs978-952-64-0116-4
Publication statusPublished - 2020
MoE publication typeG4 Doctoral dissertation (monograph)

Keywords

  • aerobic oxidation
  • copper catalysis
  • lignin
  • diastereoselective synthesis

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