1.5 Photochemistry and Radical Generation: Approaches in Mechanism Elucidation

2021 ◽  
Author(s):  
S. B. Cahoon ◽  
T. P. Yoon
Keyword(s):  
Case Studies ◽  
Organic Synthesis ◽  
Reactive Intermediates ◽  
Product Formation ◽  
Complex Reaction ◽  
Detailed Understanding ◽  
Physical Organic ◽  
Radical Generation ◽  
Complementary Techniques ◽  
Photocatalytic Reactions

AbstractThe development of photocatalytic reactions has reemerged as an active area of research in organic synthesis. A large variety of synthetically valuable transformations have now been developed that take advantage of the ease by which photocatalysts generate a variety of open-shelled reactive intermediates. The study of the mechanisms of these reactions, however, is a challenge, especially in increasingly sophisticated reactions that often involve multiple steps and complex reaction mixtures. Multiple complementary techniques often need to be utilized in tandem in order to develop a detailed understanding of these reactions. The first part of this review outlines many of the most common techniques that are used to interrogate the initiation and product-formation steps of a photocatalytic transformation. The second part describes case studies that provide contextual examples of how photophysical, electrochemical, physical organic, and computational investigations can be used together to provide insights into the mechanisms of complex photocatalytic reactions.

Recent advances in Minisci-type reactions and applications in organic synthesis

2020 ◽  
Vol 24 ◽  
Author(s):  
Wengui Wang ◽  
Shoufeng Wang
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Organic Synthesis ◽  
Radical Reactivity ◽  
Atom Loss ◽  
Radical Generation ◽  
In Situ Generation ◽  
Thermal Cleavage ◽  
Synthetic Chemist

Abstract:: Minisci-type reactions have become widely known as reactions that involve the addition of carbon-centered radicals to basic heteroarenes followed by formal hydrogen atom loss. While the originally developed protocols for radical generation remain in active use today, in recent years by a new array of radical generation strategies allow use of a wider variety of radical precursors that often operate under milder and more benign conditions. New transformations based on free radical reactivity are now available to a synthetic chemist looking to utilize a Minisci-type reaction. Radical-generation methods based on photoredox catalysis and electrochemistry, which utilize thermal cleavage or the in situ generation of reactive radical precursors, have become popular approaches. Our review will cover the remarkably literature that has appeared on this topic in recent 5 years, from 2015-01 to 2020-01, in an attempt to provide guidance to the synthetic chemist, on both the challenges that have been overcome and applications in organic synthesis.

Complex Reactions

2001 ◽  
Author(s):  
L. K. Doraiswamy
Keyword(s):  
Organic Synthesis ◽  
Product Distribution ◽  
Diels Alder ◽  
Point Of View ◽  
Complex Reaction ◽  
Design Point ◽  
Multiple Reactions ◽  
Practical Strategy ◽  
Multistep Reactions ◽  
Quantitative Treatment

When a reactant or a set of reactants undergoes several reactions (at least two) simultaneously, the reaction is said to be a complex reaction. The total conversion of the key reactant, which is used as a measure of reaction in simple reactions, has little meaning in complex reactions, and what is of primary interest is the fraction of reactant converted to the desired product. Thus the more pertinent quantity is product distribution from which the conversion to the desired product can be calculated. This is usually expressed in terms of the yield or selectivity of the reaction with respect to the desired product. From the design point of view, an equally important consideration is the analysis and quantitative treatment of complex reactions, a common example of which is the dehydration of alcohol represented by We call such a set of simultaneous reactions a complex multiple reaction. It is also important to note that many organic syntheses involve a number of steps, each carried out under different conditions (and sometimes in different reactors), leading to what we designate as multistep reactions (normally called a synthetic scheme by organic chemists). This could, for example, be a sequence of reactions like dehydration, oxidation, Diels-Alder, and hydrogenation. This chapter outlines simple procedures for the treatment of complex multiple and multistep reactions and explains the concepts of selectivity and yield. For a more detailed treatment of multiple reactions, the following books may be consulted: Aris (1969) and Nauman (1987). We conclude the chapter by considering a reaction with both catalytic and noncatalytic steps, which also constitutes a kind of complex reaction. Because both chemists and chemical engineers are involved in formulating a practical strategy for accomplishing an organic synthesis, it is important to appreciate the roles of each.

7 Electrochemically Generated Nitrogen-Centered Radicals

2022 ◽  
Author(s):  
Z.-W. Hou ◽  
H.-C. Xu
Keyword(s):  
Hydrogen Atom ◽  
Organic Synthesis ◽  
Recent Progress ◽  
Reactive Intermediates ◽  
Hydrogen Atom Abstraction ◽  
Addition Reactions ◽  
Electrochemical Generation ◽  
Nitrogen Containing Compounds

Nitrogen-centered radicals are versatile reactive intermediates for organic synthesis. This chapter describes recent progress in the electrochemical generation and reactions of nitrogen-centered radicals. Under electrochemical conditions, various nitrogen-centered radicals are generated through electrolysis of readily available precursors such as N—H bonds or azides. These reactive intermediates undergo addition reactions to π-systems or hydrogen-atom abstraction to generate various nitrogen-containing compounds.

scholarly journals Photocatalytic Atom Transfer Radical Addition to Olefins Utilizing Novel Photocatalysts

Molecules ◽  
2019 ◽  
Vol 24 (9) ◽  
pp. 1644 ◽  
Author(s):  
Errika Voutyritsa ◽  
Ierasia Triandafillidi ◽  
Nikolaos V. Tzouras ◽  
Nikolaos F. Nikitas ◽  
Eleftherios K. Pefkianakis ◽  
...  
Keyword(s):  
Metal Complexes ◽  
Organic Synthesis ◽  
Alkyl Group ◽  
Radical Addition ◽  
Bidentate Ligand ◽  
Atom Transfer ◽  
Broad Scope ◽  
Atom Transfer Radical Addition ◽  
Terpyridine Ligands ◽  
Photocatalytic Reactions

Photocatalysis is a rapidly evolving area of research in modern organic synthesis. Among the traditional photocatalysts, metal-complexes based on ruthenium or iridium are the most common. Herein, we present the synthesis of two photoactive, ruthenium-based complexes bearing pyridine-quinoline or terpyridine ligands with extended aromatic conjugation. Our complexes were utilized in the atom transfer radical addition (ATRA) of haloalkanes to olefins, using bromoacetonitrile or bromotrichloromethane as the source of the alkyl group. The tailor-made ruthenium-based catalyst bearing the pyridine-quinoline bidentate ligand proved to be the best-performing photocatalyst, among a range of metal complexes and organocatalysts, efficiently catalyzing both reactions. These photocatalytic atom transfer protocols can be expanded into a broad scope of olefins. In both protocols, the photocatalytic reactions led to products in good to excellent isolated yields.

Revisiting the ‘Phenonium Phenomenon’: Regiodivergent Opening of Nonsymmetrical Phenonium Ions with Halide Nucleophiles

Synlett ◽  
2020 ◽  
Vol 32 (01) ◽  
pp. 01-06
Author(s):  
Nicholas J. Race ◽  
Hannah M. Holst ◽  
Shelby B. McGuire
Keyword(s):  
Reactive Intermediates ◽  
Building Blocks ◽  
Stereospecific Synthesis ◽  
Neighboring Group ◽  
Group Participation ◽  
Physical Organic ◽  
Anchimeric Assistance ◽  
Neighboring Group Participation

Formation of phenonium ions through anchimeric assistance (neighboring-group participation) of aryl rings has been known since 1949. Although these reactive intermediates have been studied extensively by physical organic chemists, their potential as control elements in synthesis is underutilized. Presented here are our laboratory’s recently reported first examples of regiodivergent openings of nonsymmetrical phenonium ions with chloride nucleophiles. The selectivity of these processes is under reagent control. The reactions are operationally simple and permit the stereospecific synthesis of complex chiral building blocks from readily accessible epoxide starting materials.1 Introduction2 Select Examples of Phenonium Ion Methodology3 Regiodivergent Opening of Nonsymmetrical Phenonium Ions4 Summary and Outlook

ChemInform Abstract: New Ways of Generating Organotin Reactive Intermediates for Organic Synthesis.

ChemInform ◽  
1989 ◽  
Vol 20 (27) ◽  
Author(s):  
W. P. NEUMANN ◽  
H. HILLGAERTNER ◽  
K. M. BAINES ◽  
R. DICKE ◽  
K. VORSPOHL ◽  
...  
Keyword(s):  
Organic Synthesis ◽  
Reactive Intermediates

Aziridinyl imines in organic synthesis: Development of tandem reaction strategies and application to total synthesis of natural products

2013 ◽  
Vol 85 (4) ◽  
pp. 741-753 ◽  
Author(s):  
Hee-Yoon Lee ◽  
Seog-Beom Song ◽  
Taek Kang ◽  
Yoon Jung Kim ◽  
Su Jeong Geum
Keyword(s):  
Natural Products ◽  
Total Synthesis ◽  
Organic Synthesis ◽  
Reactive Intermediates ◽  
Diazo Compounds ◽  
Tandem Reaction ◽  
Cycloaddition Reactions ◽  
Free Radical Reactions ◽  
Sulfur Ylide ◽  
Epoxide Formation

Aziridinyl imines are well-known carbene equivalents because they are precursors of diazo compounds from which reactive intermediates can be produced. These carbene equivalents can be utilized as zwitterionic species, diradicals, or 4π system for cycloaddition reactions. Thus, the intermediates derived from aziridinyl imines have been used in the sulfur-ylide-mediated epoxide formation, tandem free-radical reactions, or cyclopropanation reaction via carbene intermediates to form trimethylenemethane (TMM) diyls, which undergo [2 + 3] cycloaddition reactions to form cyclopentanoids. Diazo compounds generated from aziridinyl imines also react with allenes to form TMM diyls. This reaction was utilized in tandem cycloaddition reactions of linear substrates to form polyquinanes. These tandem reaction strategies were successfully applied to the total synthesis of various cyclopentanoid natural products.

Synthesis of Bench-Stable N-Quaternized Ketene N,O-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis

2019 ◽  
Author(s):  
Alisha M. Blades ◽  
Danielle L. McConnell ◽  
Danielle Gomes Rodrigues ◽  
Phoebe V. Keyes ◽  
Justin C. Sonberg ◽  
...  
Keyword(s):  
Organic Synthesis ◽  
Lewis Acid ◽  
Reactive Intermediates ◽  
Electrophilic Aromatic Substitution ◽  
Preliminary Evaluation ◽  
Aromatic Substitution ◽  
Triflic Acid ◽  
Synthetic Intermediates ◽  
Nucleophilic Aromatic Substitutions

<div>N-Quaternized ketene N,O-acetals are typically an unstable, transient class of compounds most commonly observed as reactive intermediates. In this report, we describe a general approach to a variety of benchstable N-quaternized ketene N,O-acetals via treatment of pyridine or aniline bases with ethoxyacetylene and an appropriate Brønsted or Lewis acid (triflic acid, triflimide, or scandium(III) triflate). The resulting pyridinium and anilinium salts may be used as reagents or synthetic intermediates in multiple reaction types. For example, N-(1-ethoxyvinyl) pyridinium or anilinium salts can thermally release highly reactive O-ethyl ketenium ions that undergo electrophilic aromatic substitution with electron rich arenes. N-(1-ethoxyvinyl)-2-halopyridinium salts can also be utilized in peptide couplings as a derivative of Mukaiyama reagents, or react with alcohol and amines in nucleophilic aromatic substitutions.</div>

1.9 Oxygen-Centered Radicals

2021 ◽  
Author(s):  
J. Zhang ◽  
D. Liu ◽  
Y. Chen
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Organic Synthesis ◽  
Reactive Intermediates ◽  
Radical Addition ◽  
Hydrogen Atom Transfer ◽  
Reaction Conditions ◽  
Recent Advances ◽  
Carbon Carbon Bonds ◽  
Induced Reaction

AbstractOxygen-centered radicals (R1O•) are reactive intermediates in organic synthesis, with versatile synthetic utilities in processes such as hydrogen-atom transfer (HAT), β-fragmentation, radical addition to unsaturated carbon–carbon bonds, and rearrangement reactions. In this review, we focus on recent advances in the generation and transformation of oxygen-centered radicals, including (alkyl-, α-oxo-, aryl-) carboxyl, alkoxyl, aminoxyl, phenoxyl, and vinyloxyl radicals, and compare the reactivity of oxygen-centered radicals under traditional reaction conditions with their reactivity under visible-light-induced reaction conditions.

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