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Synlett

Current research reports and chronological list of recent articles..




Accounts and Rapid Communications in Synthetic Organic Chemistry: SYNLETT is an international scientific journal reporting research results and trends in synthetic organic chemistry in short personalized reviews and preliminary communications.

The publisher is Thieme. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

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Additional research articles see Current Chemistry Research Articles. Magazines with similar content (organic chemistry):

 - Beilstein Journal of Organic Chemistry.

 - European Journal of Organic Chemistry.

 - Journal of Organic Chemistry.

 - Journal of Physical Organic Chemistry.

 - Organic Letters.

 - Organic Process Research and Development.

 - Russian Journal of Organic Chemistry.



Synlett - Abstracts



Copper-Catalyzed Twofold Silylmetalation of Alkynes

The first twofold silylmetalation across a C≡C triple bond was achieved. In the presence of a catalytic amount of copper cyanide, diarylacetylenes were converted into 1,2-dimetalated 1,2-disilyl-1,2-diarylethanes on treatment with silylpotassium species generated in situ from disilane and t-BuOK. The dimetalated species were subsequently protonated to yield a series of 1,2-disilyl-1,2-diarylethanes.
Datum: 25.06.2019


An Example of Ketone Olefination via Praseodymium-Mediated Barbier Reaction in the Presence of Diethyl Phosphite

The first example of carbon double-bond formation via praseodymium-mediated Barbier type reaction of ketones and allyl halides in the presence of diethyl phosphite is reported. The reaction is highly α-regioselective and conveniently carried out under mild conditions in a one-pot fashion. From a synthetic point of view, a series of conjugated alkenes were obtained in moderate to good yields in this one-pot reaction with practical reaction conditions.
Datum: 25.06.2019


SO2F2-Promoted Dehydration of Aldoximes: A Rapid and Simple Access to Nitriles

A rapid, simple and mild process for the dehydration of aldoximes to give the corresponding nitriles, which utilizes SO2F2 as an efficient reagent, has been developed. A variety of (hetero)arene, alkene, alkyne and aliphatic aldoximes proceeded with high efficiency to afford nitriles in excellent to quantitative yields with great functional group compatibilities in acetonitrile under ambient conditions. Furthermore, an eco-friendly synthetic protocol to access nitriles from aldehydes with ortho-, meta- and para-nitrile groups was also described in aqueous methanol by using inorganic base Na2CO3, and a one-pot synthetic strategy to generate nitriles from aldehydes was proved to be feasible.
Datum: 25.06.2019


Single-Step Dual Functionalization: One-Pot Bromination-Cross-Dehydrogenative Esterification of Hydroxy Benzaldehydes with CCl3Br – A Comparison with Selectfluor

Bromination of phenolic compounds without directly using molecular bromine possesses much importance. In this article an IrIII/CCl3Br-assisted single-step double functionalization of hydroxy benzaldehydes is reported. It involves simultaneous esterification of the aldehyde group and bromination of the aryl ring of phenolic aldehydes in one-pot. The reaction proceeds under mild conditions in the presence of 445 nm blue LED light to obtain highly functionalized bromo hydroxy benzoates in moderate to good yields. In comparison, Selectfluor as an oxidant gives only non-bromo phenolic esters.
Datum: 19.06.2019


A Highly Efficient Magnetic Iron(III) Nanocatalyst for Ferrier Rearrangements

A novel and highly efficient magnetic Fe3O4@C@Fe(III) core–shell catalyst, in which the carbon shell was prepared from lotus leaf, was fabricated. This nanocatalyst was successfully applied in the synthesis of a series of 2,3-unsaturated O-glycosides in excellent yields and with high selectivity, especially in the case of 2-halo O-glycosides, which differ in reactivity from nonsubstituted O-glycosides, but which have scarcely been explored before. Moreover, the catalyst could be easily separated from the reaction by the application of an external magnetic force and reused a minimum of five times without any significant decrease in the yields of the products. In addition, the reaction proceeded readily on a gram scale, which provides a bright prospect for future applications.
Datum: 19.06.2019


Synthesis of Triazole-Fused Phenanthridines through Pd-Catalyzed Intramolecular Phenyl C–H Activation of 1,5-Diaryl-1,2,3-triazoles

An efficient method for the synthesis of triazole-fused phenanthridines from 1,5-diaryl-1,2,3-triazoles under palladium catalysis has been developed. The reaction proceeds through Pd-catalyzed intramolecular phenyl C–H activation of 1,5-diaryl-1,2,3-triazoles. This method provides a concise and efficient pathway to construct triazolo[1,5-f]phenanthridine derivatives in excellent yields.
Datum: 19.06.2019


Direct Synthesis of 1-Arylprop-1-ynes with Calcium Carbide as an Acetylene Source

A simple method is described for the synthesis of 1-arylprop-1-ynes directly from aromatic aldehyde p-tosylhydrazones by using calcium carbide as an acetylene source. The salient features of this protocol are its use of a readily available and easily handled source of acetylene, its operational simplicity, its high yield, and its broad substrate scope.
Datum: 19.06.2019


An Old Dog with New Tricks: Enjoin Wolff–Kishner Reduction for Alcohol Deoxygenation and C–C Bond Formations

The Wolff–Kishner reduction, discovered in the early 1910s, is a fundamental and effective tool to convert carbonyls into methylenes via deoxygenation under strongly basic conditions. For over a century, numerous valuable chemical products have been synthesized by this classical method. The reaction proceeds via the reversible formation of hydrazone followed by deprotonation with the strong base to give an N-anionic intermediate, which affords the deoxygenation product upon denitrogenation and protonation. By examining the mechanistic pathway of this century old classical carbonyl deoxygenation, we envisioned and subsequently developed two unprecedented new types of chemical transformations: a) alcohol deoxygenation and b) C–C bond formations with various electrophiles including Grignard-type reaction, conjugate addition, olefination, and diverse cross-coupling reactions.1 Introduction2 Background3 Alcohol Deoxygenation3.1 Ir-Catalyzed Alcohol Deoxygenation3.2 Ru-Catalyzed Alcohol Deoxygenation3.3 Mn-Catalyzed Alcohol Deoxygenation4 Grignard-Type Reactions4.1 Ru-Catalyzed Addition of Hydrazones with Aldehydes and Ketones4.2 Ru-Catalyzed Addition of Hydrazone with Imines4.3 Ru-Catalyzed Addition of Hydrazone with CO2 4.4 Fe-Catalyzed Addition of Hydrazones5 Conjugate Addition Reactions5.1 Ru-Catalyzed Conjugate Addition Reactions5.2 Fe-Catalyzed Conjugate Addition Reactions6 Cross-Coupling Reactions6.1 Ni-Catalyzed Negishi-type Coupling6.2 Pd-Catalyzed Tsuji–Trost Alkylation Reaction7 Other Reactions7.1 Olefination7.2 Heck-Type Reaction7.3 Ullmann-Type Reaction8 Conclusion and Outlook
Datum: 13.06.2019


Mechanochemically Gated Photoswitching: Expanding the Scope of Polymer Mechanochromism

Mechanophores are molecules that undergo productive, covalent chemical transformations in response to mechanical force. Over the last decade, a variety of mechanochromic mechanophores have been developed that enable the direct visualization of stress in polymers and polymeric materials through changes in color and chemiluminescence. The recent introduction of mechanochemically gated photoswitching extends the repertoire of polymer mechanochromism by decoupling the mechanical activation from the visible response, enabling the mechanical history of polymers to be recorded and read on-demand using light. Here, we discuss advances in mechanochromic mechanophores and present our design of a cyclopentadiene–maleimide Diels–Alder adduct that undergoes a force-induced retro-[4+2] cycloaddition reaction to reveal a latent diarylethene photoswitch. Following mechanical activation, UV light converts the colorless diarylethene molecule into the colored isomer via a 6π-electrocyclic ring-closing reaction. Mechanically gated photoswitching expands on the fruitful developments in mechanochromic polymers and provides a promising platform for further innovation in materials applications including stress sensing, patterning, and information storage.1 Introduction to Polymer Mechanochemistry2 Mechanochromic Reactions for Stress Sensing3 Regiochemical Effects on Mechanophore Activation4 Mechanochemically Gated Photoswitching5 Conclusions
Datum: 13.06.2019


Linked PDF of Table of Contents

Synlett 2019; 30: V-
DOI: 10.1055/s-0039-1690100



© Georg Thieme Verlag Stuttgart · New York

Artikel in Thieme eJournals:
Inhaltsverzeichnis


Datum: 13.06.2019


SYNFORM ISSUE 2019/07

Synlett 2019; 30: A97-A112
DOI: 10.1055/s-0037-1612178



© Georg Thieme Verlag KG Stuttgart · New York

Artikel in Thieme eJournals:
Inhaltsverzeichnis


Datum: 13.06.2019


Copper(II)-Promoted Oxidation/[3+2]Cycloaddition/Aromatization Cascade: Efficient Synthesis of Tetrasubstituted NH-Pyrrole from Chalcones and Iminodiacetates

A simple and highly efficient method for the preparation of tetrasubstituted NH-pyrrole from a wide range of chalcones and diethyl iminodiacetates via a Cu(OAc)2-promoted oxidation/[3+2]cycloaddition/aromatization cascade reaction has been developed. This reaction proceeds through dehydrogenations, deamination, and oxidative cyclization, affording the corresponding products in good to excellent yields. This convenient methodology for constructing tetrasubstituted NH-pyrroles has several advantages over existing methods, such as the use of easily accessible chalcones and readily available diethyl iminodiacetates, and mild reaction conditions. A wide range of substrates are tolerated.
Datum: 12.06.2019


Catalytic Asymmetric Intramolecular Bromolactonization of α,β-Unsaturated Ketones

Enantioselective bromolactonization by using an amino-urea catalyst to generate the important bromo-containing 3,4-dihydroisocoumarins is described. Excellent yields and good enantioselectivities could be achieved for various 3,4-dihydroisocoumarin compounds.
Datum: 12.06.2019


Hypervalent Iodine Mediated Efficient Solvent-Free Regioselective Halogenation and Thiocyanation of Fused N-Heterocycles

A facile, rapid, metal-free regioselective halogenation and thiocyanation of imidazo[1,2-a]pyridine/pyrimidine heterocycles has been achieved under solvent-free reaction conditions. Halogenations and thiocyanation of the heterocycles could be accomplished by simple grinding of reactants and hypervalent iodine reagents with the corresponding alkali metal or ammonium salts. The method has been extrapolated to a cleaner synthesis of brominated imidazo[1,2-a]pyridine/pyrimidine derivatives, starting from the corresponding heterocyclic amines and substituted α-bromoketones, utilising HBr generated in situ as the source of bromine.
Datum: 12.06.2019


A Photocatalyst-Free, SET-Mediated Photochemical Approach for the Synthesis of Dumbbell-Like Amine-Functionalized Bis-C60 Fullerene through C–C Bond Formation

A novel method for the synthesis of dumbbell-like amine-functionalized bis-C60 fullerene from simple bis-α-silyl tertiary benzyl amines and C60 fullerene is described. The photoreactions between bis-α-silyl tertiary benzyl amines and C60 furnished single-bonded bis-aminomethyl-1,2-dihyrofullerenes and double-bonded 1,2,5-trisubstituted bis-fulleropyrrolidines through 1,3-dipolar cycloaddition reactions of azomethine ylides under mild conditions.
Datum: 07.06.2019


1,4-Diazabicyclo[2.2.2]octane-Catalyzed Multicomponent Domino Strategy for the Synthesis of Tetrasubstituted NH-Pyrroles

A mild and efficient 1,4-diazabicyclo[2.2.2]octane (DABCO)-catalyzed three-component domino reaction was developed for the synthesis of highly functionalized NH-pyrroles from arylglyoxal monohydrates, enamino esters, and cyclic 1,3-dicarbonyl compounds in 1,4-dioxane at room temperature for 0.5 hours. Various substituted NH-pyrroles were obtained in moderate to good yields.
Datum: 07.06.2019


Synthetic Utility of One-Pot Chemoenzymatic Reaction Sequences

In recent years, there has been a rapid and sustained increase in the development and use of one-pot chemoenzymatic reaction processes for the efficient synthesis of high-value molecules. This strategy can provide a number of advantages over traditional synthetic methods, including high levels of selectivity in reactions, mild and sustainable reaction conditions, and the ability to rapidly build molecular complexity in a single reaction vessel. Here, we present several examples of chemoenzymatic one-pot reaction sequences that demonstrate the diversity of transformations that can be incorporated in these processes.
Datum: 06.06.2019


Copper Acetate Aerobic Oxidative Synthesis of Pyrido[1,2-a]benzimidazoles from Aminopyridines and Phenylboronic Acids

Pyrido[1,2-a]benzimidazoles, which show interesting and potentially useful biological activities, have drawn extensive attention from chemists. A straightforward copper acetate-oxidative one-pot synthesis of these compounds from 2-aminopyridines and phenylboronic acids through C–N bond formation and C–H bond activation was developed as a simple and convenient method.
Datum: 06.06.2019


Tricyanomethane and its Salts with Nitrogen Bases: A Correction of Sixteen Reports

A series of 16 articles, dealing with formation of tricyanomethanide salts from nitrogen bases (amines) and tricyanomethane, turned out to be wrong because no tricyanomethane or similar compounds are used and no tricyanomethanide salts are prepared. This statement is based mainly on the recently published spectroscopic data and depicted spectra, which are completely incompatible with the claimed structures. Some of the tricyanomethanide salts are now synthesized from nitrogen heterocycles and tricyanomethane or other precursors. The corresponding products show plausible spectroscopic data and physical properties, which are entirely different to those previously reported.
Datum: 05.06.2019


Development of a Hydrazine-Catalyzed Carbonyl-Olefin Metathesis Reaction

Carbonyl-olefin metathesis is a potentially powerful yet underexplored reaction in organic synthesis. In recent years, however, this situation has begun to change, most notably with the introduction of several different catalytic technologies. The development of one of those new strategies, based on hydrazine catalysts and a novel [3+2] paradigm for double bond metathesis, is discussed herein. First, the stage is set with a description of some potential applications of carbonyl-olefin metathesis and a discussion of alternative strategies for this intriguing reaction.1 Introduction2 Potential Applications of Carbonyl-Olefin Metathesis3 Carbonyl-Olefin Metathesis Strategies4 Direct (Type I): Non-Catalytic5 Direct (Type I): Acid-Catalyzed6 Indirect (Type II): Metal Alkylidenes7 Indirect (Type III): Hydrazine-Catalyzed8 Conclusion
Datum: 05.06.2019


The Allylic Acetoxylation of 1,1-Disubstituted Alkenes Catalyzed by a Palladium(II)/Monothiadiazole Ligand System

A palladium(II)/monothiadiazole ligand catalytic system and its application in catalyzing the acetoxylation of 1,1-disubstituted alkenes have been developed. With this newly designed monothiadiazole thioether ligand, the reaction showed a broad scope with respect to 1,1-disubstituted olefins, giving the corresponding products in yields of 30–86%.
Datum: 05.06.2019


Organocerium: A New Contender for Halogen–Metal Exchanges

In the context of our current research on dependable and sustainable methods for C–C bond-forming reactions, we have recently developed new strategies to generate organocerium reagents through simple bromide–cerium exchanges. n-Bu3Ce enabled a fast and general access to functionalized triaryl- and alkenyl cerium species from the corresponding aryl- and alkenyl bromides. A broad range of these new organocerium species was engaged in Zweifel’s olefination, allowing for the synthesis of widely substituted alkene derivatives in a stereospecific way. Herein, we place the formation of organocerium species in the context of known organometallic reagents (Li, Mg, Zn, Cu, Ca, La, and Sm) generated through halogen–metal exchange reactions and their application in further transformations.
Datum: 03.06.2019


Aminoxylation of Thioalkynes through Radical-Polar Crossover

A one-pot procedure for the aminoxylation of thioalkynes for the direct formation of α-functionalized thioesters under mild reaction conditions is reported. A ketenethionium ion is the key intermediate, which is generated in situ by Brønsted acid mediated protonation and undergoes a radical-polar crossover.
Datum: 03.06.2019


Synthesis of Novel C 2-Symmetric Sulfur-Based Catalysts: Asymmetric Formation of Halo- and Seleno-Functionalized Normal- and Medium-Sized Rings

The synthesis of novel, highly functionalized, C 2-symmetric sulfur-based catalysts is developed and their catalytic applications are explored in asymmetric bromo-, iodo- and seleno-functionalizations of alkenoic acids. This protocol provides the corresponding normal- and medium-sized bromo, iodo and selenolactones in up to 98% yield and 83% stereoselectivity.
Datum: 29.05.2019


Catalyst-Controlled Regio- and Stereoselective Bromolactonization with Chiral Bifunctional Sulfides

Highly regioselective 5-exo bromolactonizations of stilbene-type carboxylic acids bearing electron-withdrawing substituents are achieved for the first time via the use of chiral bifunctional sulfide catalysts possessing a urea moiety. The chiral phthalide products are obtained in moderate to good enantioselectivities as the result of 5-exo cyclizations.
Datum: 20.05.2019


Anion Metathesis in Facile Preparation of Olefin Metathesis Catalysts Bearing a Quaternary Ammonium Chloride Tag

Easy and efficient method for preparation of all-chloro ruthenium catalysts bearing a quaternary ammonium tag was developed. The key anion metathesis reaction was made with AgCl, and the facile recycling of silver wastes was demonstrated. The developed method transforms more accessible, yet poorly characterised mixed chloro/iodo Ru complexes into valuable all-chloro catalysts, useful in aqueous metathesis. Practical utility of the developed anion metathesis reaction was demonstrated by preparation of a commercial Ru catalyst, StickyCat™, on a 5 gram scale.
Datum: 20.05.2019


Diastereoselective Synthesis of γ-Lactams and δ-Lactams via a Conjugate Addition-Initiated Tandem Reaction

β-Alkoxycarbonyl-γ-lactams and γ-alkoxycarbonyl-δ-lactams were synthesized via a conjugate alkylation/Mannich reaction/lactamization tandem reaction of unsaturated dicarboxylates with diethyl zinc and aldimines. The high yield, the ready availability of the reagents, and especially the high diastereoselectivity are promising characteristics of the approach that allows access to functionalized lactams.
Datum: 20.05.2019


Acetal Metathesis: Mechanistic Insight

The origins and recent applications of acetal metathesis are discussed in the context of synthesizing polyacetals via acetal metathesis polymerization (AMP). A kinetic study of the acid-catalyzed acetal metathesis reaction suggests the rate = k[H+][acetal]2, with MeOCH2OMe and EtOCH2OEt interchanging to yield MeOCH2OEt, achieving the statistical 1:2:1 equilibrium distribution in 4 hours at 80 °C and in 1 hour at 90 °C. Upon heating 1,10-decanediol and diethoxymethane, polydecylene acetal is formed with sequential distillation of ethanol, followed by diethoxymethane. A full mechanism for this polymerization is proposed, which begins with a transacetalization sequence to convert the diol into a bisacetal, followed by acetal metathesis to yield a high-molecular-weight polymer.
Datum: 13.05.2019


Synthesis and Hybridization Properties of Covalently Mercurated and Palladated Oligonucleotides

Covalent metalation of the base moieties affords a new class of modified oligonucleotides. These organometallic oligonucleotides share many properties, notably increased hybridization affinity conferred by metal-mediated base pairing, with oligonucleotides incorporating coordinative transition-metal complexes. They are, however, set apart by their ability to retain the transition-metal ion even at extreme dilution. Such stability towards dissociation would be desirable in DNA nanotechnology and necessary in therapeutic applications. Herein we describe our efforts towards preparation and characterization of covalently mercurated and palladated oligonucleotides, highlighting in particular our recent contribution on the synthesis and potential applications of oligonucleotides incorporating dimercurated artificial nucleobases.1 Introduction2 Synthesis of Covalently Mercurated and Palladated Oligonucleotides3 Hybridization Properties of Covalently Mercurated and Palladated Oligonucleotides4 Outlook
Datum: 08.05.2019


Cp*CoIII-Catalyzed C–H Functionalization and Asymmetric Reactions Using External Chiral Sources

This account describes Cp*CoIII-catalyzed C–H functionalization reactions developed in our group between 2013 and 2018. Cp*CoIII catalysts not only serve as inexpensive alternatives to Cp*RhIII catalysts but also exhibit unique reactivity and selectivity in several transformations. In the latter part of this review, we introduce catalytic asymmetric C–H functionalization reactions using achiral RhIII or CoIII catalysts with chiral disulfonates or carboxylic acids as external chiral sources.1 Introduction and Overview2 Cp*CoIII-Catalyzed C–H Functionalization Reactions2.1 C–H Addition Reactions to Polar Double Bonds2.2 Cp*Co(CO)I2 and [Cp*CoI2]2 Precursors for the C2-selective C–H Amidation of Indoles2.3 C–H Functionalization of Carbamoyl-Protected Indoles Using Alkynes2.4 C–H Allylation Using Allyl Alcohols2.5 Cyclization Reactions of O-Acyloximes and Alkynes2.6 Other Miscellaneous Reactions3 Enantioselective C–H Functionalization Reactions by Hybrid Catalysis3.1 Cp*RhIII/Chiral Disulfonate Catalysts for the Enantioselective C–H Addition to Enones3.2 Enantioselective C–H Cleavage Using Chiral Carboxylic Acids4 Summary and Perspective
Datum: 07.05.2019


Radical Biocatalysis: Using Non-Natural Single Electron Transfer Mechanisms to Access New Enzymatic Functions

Exploiting non-natural reaction mechanisms within native enzymes is an emerging strategy for expanding the synthetic capabilities of biocatalysts. When coupled with modern protein engineering techniques, this approach holds great promise for biocatalysis to address long-standing selectivity and reactivity challenges in chemical synthesis. Controlling the stereochemical outcome of reactions involving radical intermediates, for instance, could benefit from biocatalytic solutions because these reactions are often difficult to control by using existing small molecule catalysts. General strategies for catalyzing non-natural radical reactions within enzyme active sites are, however, undeveloped. In this account, we highlight three distinct strategies developed in our group that exploit non-natural single electron transfer mechanisms to unveil previously unknown radical biocatalytic functions. These strategies allow common oxidoreductases to be used to address the enduring synthetic challenge of asymmetric hydrogen atom transfer.1 Introduction2 Photoinduced Electron Transfer from NADPH3 Ground State Electron Transfer from Flavin Hydroquinone4 Enzymatic Redox Activation in NADPH-Dependent Oxidoreductases5 Conclusion
Datum: 07.05.2019


Iterative Preparation of Platinum Nanoparticles in an Amphiphilic Polymer Matrix: Regulation of Catalytic Activity in Hydrogenation

We demonstrate that iteration of the seeded preparation of platinum nanoparticles dispersed in an amphiphilic polystyrene–poly(ethylene glycol) resin (ARP–Pt) regulates their catalytic activity in the hydrogenation of aromatic compounds in water. The catalytic activity of the fifth generation of ARP–Pt [G5] prepared through four iterations of the seeded preparation was far superior to that of the initial ARP–Pt [G1] in the hydrogenation of aromatic compounds in water.
Datum: 25.04.2019


Iterative Preparation of Platinum Nanoparticles in an Amphiphilic Polymer Matrix: Regulation of Catalytic Activity in Hydrogenation

We demonstrate that iteration of the seeded preparation of platinum nanoparticles dispersed in an amphiphilic polystyrene–poly(ethylene glycol) resin (ARP–Pt) regulates their catalytic activity in the hydrogenation of aromatic compounds in water. The catalytic activity of the fifth generation of ARP–Pt [G5] prepared through four iterations of the seeded preparation was far superior to that of the initial ARP–Pt [G1] in the hydrogenation of aromatic compounds in water.
Datum: 25.04.2019


Intermolecular Reactions of Pyridyl Radicals with Olefins via Photoredox Catalysis

Pyridines are valuable motifs in a number of bioactive and functional molecules. The chemoselective functionalization of these structures from stable and widely available starting materials is a meaningful goal. We have demonstrated selective formation of pyridyl radicals at any position (2-, 3-, 4-pyridyl), through the action of a reducing photoredox catalyst. These radicals readily engage alkenes to deliver high-value products. Alteration of the reaction medium has enabled the use of a diverse range of alkene subtypes in a highly divergent and chemoselective manner.1 Introduction2 Minisci-Type Pyridine Alkylation3 An Alternate Approach – Reductive Radical Formation4 Conjugate Addition of Pyridyl Radicals5 Radical Hydroarylation of Neutral and Rich Olefins6 Solvent-Based Chemoselectivity7 Summary and Outlook
Datum: 24.04.2019


Intermolecular Trapping of Alkoxyl Radicals with Alkenes: A New Route to Ether Synthesis

Alkoxyl radicals are highly reactive species which rapidly react by hydrogen atom transfer (HAT) or β-fragmentation to afford a carbon-centered radical. We discuss herein how these RO· radicals can be efficiently trapped in an intermolecular manner by styrene derivatives when they are generated by photoredox catalysis from the corresponding N-alkoxypyridinium salts. This allows for the synthesis of valuable ethers with complete anti-Markovnikov regioselectivity.1 Introduction2 Anti-Markovnikov Alkoxylation of Alkenes: Background3 Addition of Alkoxyl Radicals to Styrenes4 Summary and Outlook
Datum: 16.04.2019


Quick Access to Pyridines through 6π-3-Azatriene Electrocyclization: Concise Total Synthesis of Suaveoline Alkaloids

Pyridine is a prevalent structural heterocyclic motifs in natural products, pharmaceuticals, and advanced materials. Several different methodologies have been developed for the synthesis of these kinds of molecules. However, a sustainable and efficient procedure for the synthesis of pyridines is still highly desirable. In this Synpacts article, we highlight our recent approach to the construction of highly substituted pyridines though a tandem condensation/alkyne isomerization/6π-3-azatriene electrocyclization sequence. The present protocol was used to synthesize a series of polysubstituted pyridines (30 examples) in moderate to good yields. The process also permitted the development of a concise strategy for collective total syntheses of suaveoline, norsuaveoline, and macrophylline.
Datum: 15.04.2019


Consecutive Ring-Expansion Reactions for the Iterative Assembly of Medium-Sized Rings and Macrocycles

Macrocycles and medium-sized rings have important applications in several scientific fields but can be challenging to make using traditional end-to-end cyclization reactions. Ring-expansion methods represent a useful alternative and offer numerous practical benefits. In this Account, we discuss the current state of the art of ring-expansion strategies that have been applied consecutively. Such methods have the power to expedite the design and synthesis of functionalized macro­cycles via the selective, iterative insertion of smaller fragments into ring-enlarged products.1 Introduction2 Insertion Reactions2.1 Transamidation/Transpeptidation2.2 Transesterification2.3 Transthioesterification2.4 Aminyl Radical Cascade2.5 Iterative Synthesis of Lactones2.6 Successive Ring Expansion of β-Ketoesters and Lactams3 Pericyclic Reactions3.1 Sulfur-Mediated Rearrangements3.2 Nitrogen-Mediated Rearrangements4 Fragmentation Reactions5 Conclusions and Future Outlook
Datum: 12.04.2019


Consecutive Ring-Expansion Reactions for the Iterative Assembly of Medium-Sized Rings and Macrocycles

Macrocycles and medium-sized rings have important applications in several scientific fields but can be challenging to make using traditional end-to-end cyclization reactions. Ring-expansion methods represent a useful alternative and offer numerous practical benefits. In this Account, we discuss the current state of the art of ring-expansion strategies that have been applied consecutively. Such methods have the power to expedite the design and synthesis of functionalized macro­cycles via the selective, iterative insertion of smaller fragments into ring-enlarged products.1 Introduction2 Insertion Reactions2.1 Transamidation/Transpeptidation2.2 Transesterification2.3 Transthioesterification2.4 Aminyl Radical Cascade2.5 Iterative Synthesis of Lactones2.6 Successive Ring Expansion of β-Ketoesters and Lactams3 Pericyclic Reactions3.1 Sulfur-Mediated Rearrangements3.2 Nitrogen-Mediated Rearrangements4 Fragmentation Reactions5 Conclusions and Future Outlook
Datum: 12.04.2019


On Artemisinin, Cyclopamine, D-Isocitric acid, Hyperforin, Epigenetics, Sialic Acid, and More

In this Account we present the total syntheses of artemisinin (an important antimalarial agent) and cyclopamine (the first natural inhibitor of the hedgehog signaling pathway). Furthermore, we describe the design and development of a γ-butyrolactone as an inhibitor of Gcn5 (a histone N-acetyltransferase), discuss the discovery of hyperforin and guttiferon G as the first natural products acting as inhibitors of sirtuins, and present the design of inhibitors of sialic acid biosynthesis. The biomedical background and importance are also discussed. Finally, we present the discovery and development of methods for transesterification, IBX-mediated oxidations, reduction of several functional groups with LiBH4/Me3SiCl, as well as a process enabling the synthesis of kilogram amounts of D-isocitric acid and its transformation to valuable chiral derivatives.1 Artemisinin and Malaria2 Cyclopamine and Cyclops3 Sunflowers, Krebs Cycle, and Isocitric acid4 Histones and N-Acetyltransferase Gcn55 St. John’s Wort, Hippocrates, and Sirtuins6 Sialic Acid and Inhibitors of Its Biosynthesis7 Transesterification8 IBX Reloaded9 And Finally: A Small Mistake with a Big Impact10 Epilogue
Datum: 10.04.2019


Vinyl Sulfoxonium Ylide: A New Vinyl Carbenoid Transfer Reagent for the Synthesis of Heterocycles

Sulfoxonium ylides have recently gained prominence as safe carbenoid precursors in metal-catalyzed reactions. The stability and reactivity of sulfoxonium ylides depend on the substitution of the ylide carbon. The reactivity of vinyl-substituted sulfoxonium ylides is different and offers several advantages over known stabilized sulfoxonium ylides in the case of carbenoid transfer reactions. Herein, we provide an overview of early efforts in this area, with particular emphasis on our own recent development of sulfoxonium ylide-derived vinyl carbenoid transformations for N-Heterocycles.1 Introduction2 Classification of Sulfoxonium Ylides3 Synthesis of Vinyl Sulfoxonium Ylides4 [3+2] Annulation of Vinyl Sulfoxonium Ylides5 [4+1] Annulation of Vinyl Sulfoxonium Ylides6 Conclusion
Datum: 10.04.2019


Diphenyl Diselenide Catalyzed Oxidative Degradation of Benzoin to Benzoic Acid

The diphenyl diselenide catalyzed oxidative degradation of benzoin to benzoic acid is reported. As this reaction can convert the malodorous compound into an odorless and innocuous product under mild conditions, it might be useful for pollutant disposal. The reaction does not require a transition-metal catalyst or a chemical oxidant, so that it can be performed at low cost and without generation of wastes. This is believed to be the first example of the use of organoselenium catalysis technology in pollutant destruction, thereby expanding its range of applications.
Datum: 02.04.2019


Sulfoxide-Directed Iterative Assembly into Oligoarenes

A series of oligoarenes have been synthesized via sulfoxide-based iterative dehydrogenative transformations. By utilizing the sulfinyl moieties as on/off-switchable directing groups, overreactions and/or undesired oligomerizations were completely suppressed. Since the dehydrogenative couplings were not hampered by steric hinderance, sterically encumbered oligoarenes were synthesized.
Datum: 28.03.2019


Sulfoxide-Directed Iterative Assembly into Oligoarenes

A series of oligoarenes have been synthesized via sulfoxide-based iterative dehydrogenative transformations. By utilizing the sulfinyl moieties as on/off-switchable directing groups, overreactions and/or undesired oligomerizations were completely suppressed. Since the dehydrogenative couplings were not hampered by steric hinderance, sterically encumbered oligoarenes were synthesized.
Datum: 28.03.2019


Expanding the 18F-Radiochemical Space: Synthesis and Applications of 1,1-18F-Difluorinated Alkenes

The synthesis of 18F-perfluorinated motifs from [18F]fluoride is a non-trivial undertaking as highlighted by the few methods and range of motifs that are known. In this Synpacts article we highlight our recent work on the synthesis and derivatization of 1,1-18F-difluoroalkenes to expand the accessible radiochemical space with fluorine-18.1 Introduction2 Overview of the Main Strategies to Access 18F-Perfluorinated Motifs with [18F]Fluoride3 1,1-18F-Difluoroalkenes4 Conclusion
Datum: 25.03.2019


Selective Protection of Secondary Alcohols by Using Formic Acid as a Mild and Efficient Deprotection Reagent for Primary tert-Butyldimethylsilyl Ethers

A mild, efficient, and environmentally friendly method for the selective protection of secondary hydroxyl groups is described. The method involves the protection of both primary and secondary hydroxyl groups as tert-butyldimethylsilyl (TBDMS) ethers and selective deprotection of the primary TBDMS group with formic acid in acetonitrile/water. The rates of desilylation of primary and secondary TBDMS ethers by different concentrations of formic acid are determined. Formic acid of 5–20% concentration is found to selectively deprotect primary TBDMS ethers while keeping more than 95% of their secondary counterparts intact.
Datum: 19.03.2019


Sodium Selenosulfate from Sodium Sulfite and Selenium Powder: An Odorless Selenylating Reagent for Alkyl Halides to Produce Dialkyl Diselenide Catalysts

Na2SeSO3, which can be generated in situ by the reaction of Na2SO3 with Se power, was found to be an odorless reagent for the selenenylation of alkyl halides to produce dialkyl diselenides. These products have been recently shown to be good catalysts for the Baeyer–Villiger oxidation of carbonyl compounds, for the selective oxidation of alkenes, or for the oxidative deoximation of oximes. By using aqueous EtOH as the solvent and avoiding the generation of a malodourous selenol intermediate, the selenylation reaction with Na2SeSO3 is much more environmentally friendly than conventional methods. Owing to the cheap and abundant starting materials and selenium reagents, our novel synthetic method reduces the production costs of dialkyl diselenides as organoselenium catalysts, thereby advancing practical applications of organoselenium-catalysis technologies.
Datum: 07.02.2019


Organoselenium-Catalyzed Polymerization of Aniline with Hydrogen Peroxide as Oxidant

A convenient method for the synthesis of polyanilines was developed through the organoselenium-catalyzed oxidation of anilines with H2O2. Unlike reported methods, this reaction generates no wastes other than water. These green features make the method much more practical in terms of large-scale preparation. Moreover, it is the first example of an application of organoselenium catalysis techniques in aniline polymerization reactions and might be an important advance in the fields of both organoselenium catalysis and polyanilines.
Datum: 05.02.2019


Thiolate-Initiated Synthesis of Dibenzothiophenes from 2,2′-Bis(methylthio)-1,1′-Biaryl Derivatives through Cleavage of Two Carbon–Sulfur Bonds

A catalytic reaction involving the cleavage of two carbon–sulfur bonds in 2,2′-bis(methylthio)-1,1′-biaryl derivatives is reported. This reaction does not require a transition-metal catalyst and is promoted by a thiolate anion. Notably, based on DFT calculations, the product-forming cyclization step is shown to proceed through a concerted nucleophilic aromatic substitution (CSNAr) mechanism.
Datum: 14.01.2019


 


Category: Current Chemistry Research

Last update: 28.03.2018.






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