Regio- and stereoselectivity of oxidative coupling reactions of phenols. Spirodienones as construction units in lignin

Dissertation

Research output: ThesisDissertationCollection of Articles

1 Citation (Scopus)

Abstract

Dimeric phenolic compounds - lignans and dilignols - form in the so-called oxidative coupling reaction of phenols. Enzymes such as peroxidases and laccases catalyze the reaction using hydrogen peroxide or oxygen, respectively, as oxidant generating phenoxy radicals which couple together according to certain rules. In this thesis, the effects of the structures of starting materials - monolignols - and the effects of reaction conditions such as pH and solvent system on this coupling mechanism and on its regio- and stereoselectivity have been studied. After the primary coupling of two phenoxy radicals a very reactive quinone methide intermediate is formed. This intermediate reacts quickly with a suitable nucleophile which can be, for example, an intramolecular hydroxyl group or another nucleophile such as water, methanol, or a phenolic compound in the reaction system. This reaction is catalyzed by acids. After the nucleophilic addition to the quinone methide, other hydrolytic reactions, rearrangements, and elimination reactions occur, leading finally to stable dimeric structures called lignans or dilignols. Similar reactions occur also in the so-called lignification process when monolignol (or dilignol) reacts with the growing lignin polymer. New kinds of structures have been observed in this thesis. The dimeric compounds with a so-called spirodienone structure have been observed to form both in the dehydrodimerization of methyl sinapate and in the -1-type cross-coupling reaction of two different monolignols. This -1-type dilignol with a spirodienone structure was the first synthesized and published dilignol model compound, and at present, it has been observed to exist as a fundamental construction unit in lignins. The enantioselectivity of the oxidative coupling reaction was also studied for obtaining enantiopure lignans and dilignols. A rather good enantioselectivity was obtained in the oxidative coupling reaction of two monolignols with chiral auxiliary substituents using peroxidase/H2O2 as an oxidation system. This observation was published as one of the first enantioselective oxidative coupling reaction of phenols. Pure enantiomers of lignans were also obtained by using chiral cryogenic chromatography as a chiral resolution technique. This technique was shown to be an alternative route to obtain enantiopure lignans or lignin model compounds in a preparative scale.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • University of Helsinki
Supervisors/Advisors
  • Brunow, Gösta, Supervisor, External person
Award date27 Sep 2008
Place of PublicationEspoo
Publisher
Print ISBNs978-951-38-7110-9
Electronic ISBNs978-951-38-7111-6
Publication statusPublished - 2008
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

Stereoselectivity
Regioselectivity
Lignans
Lignin
Phenols
Nucleophiles
Enantioselectivity
Peroxidases
Laccase
Enantiomers
Chromatography
Oxidants
Hydroxyl Radical
Cryogenics
Hydrogen Peroxide
Peroxidase
Methanol
Polymers
Oxygen
Oxidation

Keywords

  • regioselectivity
  • stereoselectivity
  • oxidative coupling reactions
  • phenols
  • spirodienones
  • lignans
  • dilignols
  • dehydrodimerization
  • peroxidases
  • chirality
  • pH
  • catalysis

Cite this

@phdthesis{4283f5c7774a4b79a61483dbb8fefce4,
title = "Regio- and stereoselectivity of oxidative coupling reactions of phenols. Spirodienones as construction units in lignin: Dissertation",
abstract = "Dimeric phenolic compounds - lignans and dilignols - form in the so-called oxidative coupling reaction of phenols. Enzymes such as peroxidases and laccases catalyze the reaction using hydrogen peroxide or oxygen, respectively, as oxidant generating phenoxy radicals which couple together according to certain rules. In this thesis, the effects of the structures of starting materials - monolignols - and the effects of reaction conditions such as pH and solvent system on this coupling mechanism and on its regio- and stereoselectivity have been studied. After the primary coupling of two phenoxy radicals a very reactive quinone methide intermediate is formed. This intermediate reacts quickly with a suitable nucleophile which can be, for example, an intramolecular hydroxyl group or another nucleophile such as water, methanol, or a phenolic compound in the reaction system. This reaction is catalyzed by acids. After the nucleophilic addition to the quinone methide, other hydrolytic reactions, rearrangements, and elimination reactions occur, leading finally to stable dimeric structures called lignans or dilignols. Similar reactions occur also in the so-called lignification process when monolignol (or dilignol) reacts with the growing lignin polymer. New kinds of structures have been observed in this thesis. The dimeric compounds with a so-called spirodienone structure have been observed to form both in the dehydrodimerization of methyl sinapate and in the -1-type cross-coupling reaction of two different monolignols. This -1-type dilignol with a spirodienone structure was the first synthesized and published dilignol model compound, and at present, it has been observed to exist as a fundamental construction unit in lignins. The enantioselectivity of the oxidative coupling reaction was also studied for obtaining enantiopure lignans and dilignols. A rather good enantioselectivity was obtained in the oxidative coupling reaction of two monolignols with chiral auxiliary substituents using peroxidase/H2O2 as an oxidation system. This observation was published as one of the first enantioselective oxidative coupling reaction of phenols. Pure enantiomers of lignans were also obtained by using chiral cryogenic chromatography as a chiral resolution technique. This technique was shown to be an alternative route to obtain enantiopure lignans or lignin model compounds in a preparative scale.",
keywords = "regioselectivity, stereoselectivity, oxidative coupling reactions, phenols, spirodienones, lignans, dilignols, dehydrodimerization, peroxidases, chirality, pH, catalysis",
author = "Harri Set{\"a}l{\"a}",
year = "2008",
language = "English",
isbn = "978-951-38-7110-9",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
number = "689",
address = "Finland",
school = "University of Helsinki",

}

Regio- and stereoselectivity of oxidative coupling reactions of phenols. Spirodienones as construction units in lignin : Dissertation. / Setälä, Harri.

Espoo : VTT Technical Research Centre of Finland, 2008. 141 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Regio- and stereoselectivity of oxidative coupling reactions of phenols. Spirodienones as construction units in lignin

T2 - Dissertation

AU - Setälä, Harri

PY - 2008

Y1 - 2008

N2 - Dimeric phenolic compounds - lignans and dilignols - form in the so-called oxidative coupling reaction of phenols. Enzymes such as peroxidases and laccases catalyze the reaction using hydrogen peroxide or oxygen, respectively, as oxidant generating phenoxy radicals which couple together according to certain rules. In this thesis, the effects of the structures of starting materials - monolignols - and the effects of reaction conditions such as pH and solvent system on this coupling mechanism and on its regio- and stereoselectivity have been studied. After the primary coupling of two phenoxy radicals a very reactive quinone methide intermediate is formed. This intermediate reacts quickly with a suitable nucleophile which can be, for example, an intramolecular hydroxyl group or another nucleophile such as water, methanol, or a phenolic compound in the reaction system. This reaction is catalyzed by acids. After the nucleophilic addition to the quinone methide, other hydrolytic reactions, rearrangements, and elimination reactions occur, leading finally to stable dimeric structures called lignans or dilignols. Similar reactions occur also in the so-called lignification process when monolignol (or dilignol) reacts with the growing lignin polymer. New kinds of structures have been observed in this thesis. The dimeric compounds with a so-called spirodienone structure have been observed to form both in the dehydrodimerization of methyl sinapate and in the -1-type cross-coupling reaction of two different monolignols. This -1-type dilignol with a spirodienone structure was the first synthesized and published dilignol model compound, and at present, it has been observed to exist as a fundamental construction unit in lignins. The enantioselectivity of the oxidative coupling reaction was also studied for obtaining enantiopure lignans and dilignols. A rather good enantioselectivity was obtained in the oxidative coupling reaction of two monolignols with chiral auxiliary substituents using peroxidase/H2O2 as an oxidation system. This observation was published as one of the first enantioselective oxidative coupling reaction of phenols. Pure enantiomers of lignans were also obtained by using chiral cryogenic chromatography as a chiral resolution technique. This technique was shown to be an alternative route to obtain enantiopure lignans or lignin model compounds in a preparative scale.

AB - Dimeric phenolic compounds - lignans and dilignols - form in the so-called oxidative coupling reaction of phenols. Enzymes such as peroxidases and laccases catalyze the reaction using hydrogen peroxide or oxygen, respectively, as oxidant generating phenoxy radicals which couple together according to certain rules. In this thesis, the effects of the structures of starting materials - monolignols - and the effects of reaction conditions such as pH and solvent system on this coupling mechanism and on its regio- and stereoselectivity have been studied. After the primary coupling of two phenoxy radicals a very reactive quinone methide intermediate is formed. This intermediate reacts quickly with a suitable nucleophile which can be, for example, an intramolecular hydroxyl group or another nucleophile such as water, methanol, or a phenolic compound in the reaction system. This reaction is catalyzed by acids. After the nucleophilic addition to the quinone methide, other hydrolytic reactions, rearrangements, and elimination reactions occur, leading finally to stable dimeric structures called lignans or dilignols. Similar reactions occur also in the so-called lignification process when monolignol (or dilignol) reacts with the growing lignin polymer. New kinds of structures have been observed in this thesis. The dimeric compounds with a so-called spirodienone structure have been observed to form both in the dehydrodimerization of methyl sinapate and in the -1-type cross-coupling reaction of two different monolignols. This -1-type dilignol with a spirodienone structure was the first synthesized and published dilignol model compound, and at present, it has been observed to exist as a fundamental construction unit in lignins. The enantioselectivity of the oxidative coupling reaction was also studied for obtaining enantiopure lignans and dilignols. A rather good enantioselectivity was obtained in the oxidative coupling reaction of two monolignols with chiral auxiliary substituents using peroxidase/H2O2 as an oxidation system. This observation was published as one of the first enantioselective oxidative coupling reaction of phenols. Pure enantiomers of lignans were also obtained by using chiral cryogenic chromatography as a chiral resolution technique. This technique was shown to be an alternative route to obtain enantiopure lignans or lignin model compounds in a preparative scale.

KW - regioselectivity

KW - stereoselectivity

KW - oxidative coupling reactions

KW - phenols

KW - spirodienones

KW - lignans

KW - dilignols

KW - dehydrodimerization

KW - peroxidases

KW - chirality

KW - pH

KW - catalysis

M3 - Dissertation

SN - 978-951-38-7110-9

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -