scholarly journals Semiconductors as sensitisers for the radical addition of tertiary amines to electron deficient alkenes

2003 ◽  
Vol 5 (3) ◽  
pp. 175-182 ◽  
Author(s):  
Siniša Marinković ◽  
Norbert Hoffmann
Keyword(s):  
Electron Transfer ◽  
Organic Synthesis ◽  
Radical Reaction ◽  
Heterogeneous Photocatalysis ◽  
Radical Addition ◽  
Point Of View ◽  
Tertiary Amines ◽  
Radical Intermediate ◽  
Radical Chain ◽  
High Yields

Using heterogeneous photocatalysis, the radical addition of tertiary amines with electron deficient alkenes can be performed in high yields (up to 98%) and high facial diastereoselectivity. The photochemical induced electron transfer process initiates the radical chain reaction and inorganic semiconductors likeTiO2and ZnS were used. According to the proposed mechanism, the reaction takes place at the surface of the semiconductor and the termination step results from an interfacial electron transfer from the conduction band to the oxoallyl radical intermediate. Frequently, semiconductors are used for the mineralisation of organic compounds in wastewater. However, in this case, they are used in organic synthesis. The process can be performed in a convenient way and is particularly interesting from the ecological and economical point of view. No previous functionalization of the tertiary amines is necessary for C − C bond formation. Further on, the amines are used both as reactant and as solvent. The excess is recycled by distillation and the inexpensive sensitiser can be easily removed by filtration. In this way, products of high interest for organic synthesis are obtained by a diastereoselective radical reaction.

Photochemically induced radical addition of tertiary amines to C=C and C=O double bonds: A green chemistry contribution to organic synthesis

2007 ◽  
Vol 79 (11) ◽  
pp. 1949-1958 ◽  
Author(s):  
Norbert Hoffmann
Keyword(s):  
Electron Transfer ◽  
Green Chemistry ◽  
Organic Synthesis ◽  
Organic Molecules ◽  
Redox Chemistry ◽  
Heterogeneous Photocatalysis ◽  
Radical Addition ◽  
Tertiary Amines ◽  
Double Bonds ◽  
Alkyl Radicals

Photochemically induced electron transfer considerably enriches the redox chemistry of organic molecules. This primary step has been used to produce α-amino alkyl radicals that can be added to various double bonds. The addition to olefinic and carbonyl bonds is discussed. Homogeneous and heterogeneous photocatalysis methods with various electron-transfer sensitizers are described.

Efficient radical addition of tertiary amines to alkenes using photochemical electron transfer

2006 ◽  
Vol 78 (12) ◽  
pp. 2227-2246 ◽  
Author(s):  
Norbert Hoffmann ◽  
Samuel Bertrand ◽  
Siniša Marinković ◽  
Jens Pesch
Keyword(s):  
Electron Transfer ◽  
Tertiary Amine ◽  
Pyrrolizidine Alkaloids ◽  
Isotopic Labeling ◽  
Heterogeneous Photocatalysis ◽  
Radical Addition ◽  
Mechanistic Study ◽  
Tertiary Amines ◽  
Cyclization Reactions ◽  
Inorganic Semiconductors

An efficient photoinduced radical addition of tertiary amine, mainly cyclic derivatives, to electron-deficient alkenes was developed. The reaction was applied to the asymmetric synthesis of the pyrrolizidine alkaloids laburnine and isoretronecanol. The method was then optimized for the addition of a larger variety of tertiary amines, in particular acyclic ones. Radical tandem addition cyclization reactions with unsaturated tertiary amines have also been investigated. A detailed mechanistic study using isotopic labeling enabled the optimization of a corresponding reaction with N,N-dialkylaniline derivatives. The origin of the high reaction stereoselectivity achieved with menthyloxyfuranone was elucidated. The radical addition of tertiary amines was also performed with heterogeneous photocatalysis using inorganic semiconductors as sensitizers.

Efficient Radical Addition of Tertiary Amines to Alkenes Using Photochemical Electron Transfer

ChemInform ◽  
2007 ◽  
Vol 38 (21) ◽  
Author(s):  
Norbert Hoffmann ◽  
Samuel Bertrand ◽  
Sinisa Marinkovic ◽  
Jens Pesch
Keyword(s):  
Electron Transfer ◽  
Radical Addition ◽  
Tertiary Amines

scholarly journals The reduction of α-bromocamphor by tertiary amines

1992 ◽  
Vol 70 (1) ◽  
pp. 173-176 ◽  
Author(s):  
Jian Jeffrey Chen ◽  
Dennis D. Tanner
Keyword(s):  
Electron Transfer ◽  
Free Radical ◽  
Chain Termination ◽  
Tertiary Amines ◽  
Chain Mechanism ◽  
Chain Reaction ◽  
Radical Chain ◽  
Electron Transfer Chain ◽  
Chain Sequence ◽  
Transfer Chain

The reduction of α-bromocamphor to camphor by N,N-dimethylaniline (DMA) at high temperatures (> 200 °C) proceeds via a free radical chain sequence. The reduction can be effected with DMA or triethylamine (TEA) in acetonitrile at much lower temperatures in the presence of di-tert-butylperoxide. The chain termination step is the dimerization of the camphor radical. These reductions presumably constitute an example of an electron transfer chain mechanism involving a tertiary amine as the chain propagating species. Keywords: reduction, tertiary amines, α-bromocamphor, chain reaction.

Studies on electrooxidation of lignin and lignin model compounds. Part 1: Direct electrooxidation of non-phenolic lignin model compounds

Holzforschung ◽  
2012 ◽  
Vol 66 (3) ◽  
Author(s):  
Takumi Shiraishi ◽  
Toshiyuki Takano ◽  
Hiroshi Kamitakahara ◽  
Fumiaki Nakatsubo
Keyword(s):  
Electron Transfer ◽  
Cyclic Voltammetry ◽  
Carbonyl Compounds ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Bulk Electrolysis ◽  
Lignin Model ◽  
Dimeric Compound ◽  
High Yields ◽  
Short Time

Abstract The direct anodic oxidation of non-phenolic lignin model compounds was investigated to understand their basic behaviors. The results of cyclic voltammetry (CV) studies of monomeric model, such as 1-(4-ethoxy-3-methoxyphenyl)ethanol, are interpreted as the oxidation for Cα-carbonylation did not proceed in the reaction without a catalyst, but a base promotes this reaction. Indeed, the bulk electrolyses of the monomeric lignin model compounds with 2,6-lutidine afforded the corresponding Cα-carbonyl compounds in high yields (60–80%). It is suggested that deprotonation at Cα-H in the ECEC mechanism (E=electron transfer and C=chemical step) is important for Cα-carbonylation. In the uncatalyzed bulk electrolysis of a β-O-4 model dimeric compound, 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether, the corresponding Cα-carbonyl compound was not detected but as a result of Cα-Cβcleavage 4-O-ethylvanillin was found in 40% yield. In the electrolysis reaction in the presence of 2,6-lutidine (as a sterically hindered light base), the reaction stopped for a short time unexpectedly. These results indicate the different electrochemical behavior of simple monomeric model compounds and dimeric β-O-4 models. The conclusion is that direct electrooxidation is unsuitable for Cα-carbonylation of lignin.

UV-Light-Induced Dehydrogenative N-Acylation of Amines with 2-Nitrobenzaldehydes to Give 2-Aminobenzamides

Synthesis ◽  
2022 ◽  
Author(s):  
Dishu Zeng ◽  
Tianbao Yang ◽  
Niu Tang ◽  
Wei Deng ◽  
Jiannan Xiang ◽  
...  
Keyword(s):  
Amino Acid ◽  
Organic Synthesis ◽  
Efficient Method ◽  
Building Block ◽  
Room Temperature ◽  
Uv Light ◽  
Amino Acid Derivatives ◽  
One Pot ◽  
Plausible Mechanism ◽  
High Yields

A simple, mild, green and efficient method for the synthesis of 2-aminobenzamides was highly desired in organic synthesis. Herein, we developed an efficient, one-pot strategy for the synthesis of 2-aminobenzamides with high yields irradiated by UV light. 32 examples proceeded successfully by this photo-induced protocol. The yield reached up to 92%. The gram scale was also achieved easily. This building block could be applied in the preparation of quinazolinones derivatives. Amino acid derivatives could be employed smoothly at room temperature. Finally, a plausible mechanism was proposed.

scholarly journals Light-Driven Depolymerization of Native Lignin Enabled by Proton- Coupled Electron Transfer

2019 ◽  
Author(s):  
Suong Nguyen ◽  
Phillip Murray ◽  
Robert Knowles
Keyword(s):  
Electron Transfer ◽  
Visible Light ◽  
Bond Cleavage ◽  
Direct Conversion ◽  
Alkoxy Radical ◽  
Radical Intermediate ◽  
Polymer Backbone ◽  
Good Efficiency ◽  
Chemical Reagents ◽  
Proton Coupled Electron Transfer

<div><p>Here we report a catalytic, light-driven method for the redox-neutral depolymerization of native lignin biomass at ambient temperature. This transformation proceeds via a proton-coupled electron-transfer (PCET) activation of an alcohol O–H bond to generate a key alkoxy radical intermediate, which then drives the <i>β</i>-scission of a vicinal C–C bond. Notably, this depolymerization is driven solely by visible light irradiation, requiring no stoichiometric chemical reagents and producing no stoichiometric waste. This method exhibits good efficiency and excellent selectivity for the activation and fragmentation of <i>β</i>-O-4 linkages in the polymer backbone, even in the presence of numerous other PCET-active functional groups. DFT analysis suggests that the key C–C bond cleavage reactions produce non-equilibrium product distributions, driven by excited-state redox events. These results provide further evidence that visible-light photocatalysis can serve as a viable method for the direct conversion of lignin biomass into valuable arene feedstocks.</p></div>

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