Carbon-heteroatom Bond Formation Research Articles

To Protonate or Alkylate? Stereoselective Brønsted Acid Catalysis of CC Bond Formation Using Diazoalkanes

A new means to activate diazoalkanes has been discovered and applied broadly over the past few years. Brønsted acids, both achiral and chiral, have been used to promote the formation of carbon-carbon and carbon-heteroatom bonds with a growing number of diazoalkane derivatives. Aside from their straightforward ability to build structural and stereochemical complexity in innovative new ways, these transformations are remarkable owing to their ability to skirt competitive diazo protonation--a reaction that has long been used to prepare esters efficiently and cleanly from carboxylic acids. In cases where achiral Brønsted acids are used, high diastereoselection can be achieved. Meanwhile, chiral Brønsted acids can deliver products with both high diastereo- and enantioselectivity. More recently, systems have emerged that combine Brønsted acids and either Lewis acids or transition metals to promote carbon-carbon bond formation from diazoalkanes.

Biaryl Phosphites: New Efficient Adaptative Ligands for Pd-Catalyzed Asymmetric Allylic Substitution Reactions

Pharmaceuticals, agrochemicals, fragrances, fine chemicals, and natural product chemistry all rely on the preparation of enantiomerically enriched compounds. The palladium-catalyzed asymmetric allylic substitution, which allows for the enantioselective formation of carbon-carbon and carbon-heteroatom bonds, is a potential synthetic tool for preparing these compounds. To date, most of the successful ligands reported for the Pd-catalyzed allylic substitution reactions have used three main design strategies. The first, developed by Hayashi and co-workers, used a secondary interaction of the nucleophile with a side chain of the ligand to direct the approach of the nucleophile to one of the allylic terminal carbon atoms. The second increased the ligand's bite angle in order to create a chiral cavity in which the allyl system is perfectly embedded. To discriminate electronically between the two allylic terminal carbon atoms, the third strategy employed heterodonor ligands. Although many chiral ligands have been successfully applied in the substitution of several disubstituted substrates, problems generally remain with both substrate specificity and reaction rates using these methods. Other substrates, such as those that are monosubstituted, will require more active and more regio- and enantioselective Pd-catalysts. Overcoming these limitations requires research toward the development of new ligands. This Account discusses the application of homo- and heterodonor biaryl-containing phosphites as new, versatile, and highly effective ligands in the Pd-catalyzed asymmetric allylic substitution of several substrate types. We and others recently demonstrated that the inclusion of biarylphosphite moieties in ligand design is highly advantageous. In these systems, the catalyst's substrate specificity decreases because the chiral pocket created (the chiral cavity with the embedded allyl ligand) is flexible enough to allow the perfect coordination of hindered and unhindered substrates. Reaction rates with these ligands increase because of the larger pi-acceptor ability of these moieties. The ability of the phosphite moiety to accept pi-electrons and enhance the S(N)1 character of the nucleophilic attack increases the regioselectivity of the reactions toward the desired branched isomer in monosubstituted linear substrates. Finally, the easy synthesis of biaryl phosphites from readily available alcohols allows for simple ligand tuning as well as systematic modifications of several important ligand parameters. Taking advantage of these features, we and others have designed highly adaptative biaryl-phosphite-containing ligands for asymmetric Pd-allylic substitution reactions. In this context, several diphosphites, phosphite-oxazolines, and phosphite-phosphoroamidites have recently emerged as extremely effective ligands for this process. Using a broad range of mono- and disubstituted hindered and unhindered linear and cyclic substrates, we have obtained high activities (turnover frequencies up to 22,000 mol substrate x (mol Pd x h)(-1)) unprecedented in the literature along with excellent regio- (up to 99%) and enantioselectivitites (up to >99%) at low catalyst loadings (turnover numbers up to 10,000 mol substrate x (mol Pd x h)(-1)). Appropriate ligand tuning allows access to both enantiomers of the substitution products.

Anodic oxidations and polarity: exploring the chemistry of olefinic radical cations

The cyclization chemistry of radical cations derived from electron-rich olefins has been examined and the relationship between the polarization of the radical cation and the chemoselectivity of the reaction probed. It was found that more polarized radical cations favor carbon–carbon bond formation while less polarized radical cations favor carbon–heteroatom bond formation. A new approach to the synthesis of quaternary carbons was uncovered and the compatibility of ene diol ethers with anodic olefin coupling reactions examined.

Manganese(III)-promoted reactions for formation of carbon–heteroatom bonds

Manganese(III) reagent is an important one- electron oxidant for initiation of free-radical reactions and formation of carbon-carbon bonds. The reactions are usually carried out under mild conditions, have high regio- and stereo-selectivities, and good functional group tolerance. Summarized in this article are the developments of manganese (III)-based reactions for the formation of carbon-heteroatom bonds including carbon-oxygen, carbon-phosphorus, carbon-sulfur, and carbon-nitrogen bonds, and their applications for the synthesis of related heterocyclic systems.

Selective Benzylic and Allylic Alkylation of Protic Nucleophiles with Sulfonamides through Double Lewis Acid Catalyzed Cleavage of sp3 Carbon–Nitrogen Bonds

The acid-catalyzed benzylic and allylic alkylation of protic nucleophiles is fundamentally important for the formation of carbon-carbon and carbon-heteroatom bonds, and it is a formidable challenge for benzylic and allylic amine derivatives to be used as the alkylating agents. Herein we report a highly efficient benzylic and allylic alkylation of protic carbon and sulfur nucleophiles with sulfonamides through double Lewis acid catalyzed cleavage of sp(3) carbon-nitrogen bonds at room temperature. In the presence of a catalytic amount of inexpensive ZnCl(2)-TMSCl (TMSCl: chlorotrimethylsilane), 1,3-diketones, beta-keto esters, beta-keto amides, malononitrile, aromatic compounds, thiols, and thioacetic acid can couple with a broad range of tosyl-activated benzylic and allylic amines to give diversely functionalized products in good to excellent yields and with high regioselectivity. Furthermore, the cross-coupling reaction of 1,3-dicarbonyl compounds with benzylic propargylic amine derivatives has been successfully applied to the one-step synthesis of polysubstituted furans and benzofurans.

ChemInform Abstract: Stereodefined Synthesis of a New Type of 1,3‐Dienes by Ligand‐Controlled Carbon—Carbon and Carbon—Heteroatom Bond Formation in Nickel‐Catalyzed Reaction of Diaryldichalcogenides with Alkynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Recent Advances in Iron Catalysis in Organic Synthesis

Transition metal complexes play a vital role as catalysts in organic syntheses, enhancing selectivity and rates of many transformations. Typically iron is not the first choice when it comes to development of novel catalyst systems. However, iron has a number of advantages to other transition metals typically used in catalysis: iron is cheap, non-toxic, environmentally friendly and abundant. Accordingly, an increasing number of publications describe novel applications of iron catalysts in organic synthesis. The review article covers recent developments in the field since 2004. Iron catalysis in carbon-carbon bond formations, cyclizations, carbon-heteroatom bond formation, oxidations, biomimetic oxidations, reductions and polymerizations is summarized. The article demonstrates the versatility of iron in organic synthesis and the vigorous research activities in the area.

Carbon–heteroatom bond formation catalysed by organometallic complexes

At one time the synthetic chemist's last resort, reactions catalysed by transition metals are now the preferred method for synthesizing many types of organic molecule. A recent success in this type of catalysis is the discovery of reactions that form bonds between carbon and heteroatoms (such as nitrogen, oxygen, sulphur, silicon and boron) via complexes of transition metals with amides, alkoxides, thiolates, silyl groups or boryl groups. The development of these catalytic processes has been supported by the discovery of new elementary reactions that occur at metal-heteroatom bonds and by the identification of factors that control these reactions. Together, these findings have led to new synthetic processes that are in daily use and have formed a foundation for the development of processes that are likely to be central to synthetic chemistry in the future.

Carbon−Nitrogen Bond Formation Involving Well-Defined Aryl−Copper(III) Complexes

Carbon-heteroatom bond formation from copper(III) is commonly invoked as a key step in catalytic reactions, including the century-old Ullmann reactions. Well-defined examples of such reactions have never been observed. Here, we demonstrate that a well-defined Cu(III)-aryl species reacts with a variety nitrogen nucleophiles to undergo facile carbon-nitrogen bond formation.

ChemInform Abstract: Palladium‐ and Copper‐Catalyzed Arylation Reactions in the Presence of Water, with a Focus on Carbon—Heteroatom Bond Formation

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Palladium and copper-catalysed arylation reactions in the presence of water, with a focus on carbon–heteroatom bond formation

Palladium and copper-catalysed arylation of amines, alcohols and thiols, powerful tools for the construction of C-N, C-O and C-S bonds, are typically carried out in organic (and often toxic) solvents. Therefore the use of such a sustainable, benign solvent as water in this context has gained growing attention. This tutorial review presents the most recent advances dealing with palladium and copper-catalysed carbon-heteroatom bond formation performed in total or partial aqueous media. The particular and distinctive features of water which are apparently responsible for the acceleration and greater chemoselectivity of the aqueous protocols will also be discussed.

Metal-catalyzed nucleophilic carbon–heteroatom (C–X) bond formation: the role of M–X intermediates

Many important reactions that lead to carbon-heteroatom bond formation involve attack of anionic heteroatom nucleophiles, such as hydroxides, alkoxides, amides, thiolates and phosphides, at carbon. Related catalytic transformations are mediated by late transition metal complexes of these groups, which remain nucleophilic on metal coordination as a result of repulsive filled-filled interactions between the heteroatom lone pairs and metal d-orbitals and/or of polarization of the bonds Mdelta+-Xdelta-. This Perspective presents examples of catalytic nucleophilic C-X bond formation in both biological and synthetic systems and describes how changes in the metal, ancillary ligands and X groups may be used to tune nucleophilic reactivity.

Synthesis of β-Functionalized Porphyrins via Palladium-Catalyzed Carbon−Heteroatom Bond Formations: Expedient Entry into β-Chiral Porphyrins

A procedure was developed for the preparation of beta-monobromo-tetraphenylporphyrin (BrTPP) in a greatly improved yield from the selective bromination of tetraphenylporphyrin (TPP) by NBS. BrTPP was successfully employed as a versatile synthon for convenient synthesis of a wide range of beta-monofunctionalized porphyrins with various heteroatom functionalities via palladium-mediated carbon-heteroatom bond formations. Examples include beta-amino, -amido, -oxo, and -mercaptoporphyrins from reactions with amines, amides, alcohols, and thiols, respectively. Applying the synthetic approach to chiral amides, beta-chiral porphyrins were effectively constructed.

Click Chemistry - What’s in a Name? Triazole Synthesis and Beyond

The environmentally amiable route to carbon-heteroatom bond formation, described by Sharpless as ‘click chemistry’, has become known as a fast, efficient, and reliable approach to the synthesis of novel compounds with desired functionalities. Readily available starting materials must be used in this methodology and they should be essentially inert to most biological and organic conditions, including water and molecular oxygen. In this review, we cover reactions included in this label such as cycloadditions, nucleophilic ring-opening reactions of strained cycles, and amide synthesis, as well as their applications in organic synthesis, molecular biology, macromolecular chemistry and materials science.

New synthetic technology for the construction of N-hydroxyindoles and synthesis of nocathiacin I model systems

A new synthetic method providing expedient access to a wide range of polyfunctionalized N-hydroxyindoles ( IV) is reported. These unique constructs are assembled by nucleophilic additions to in situ generated α,β-unsaturated nitrones ( III) through carbon–carbon and carbon–heteroatom bond formation. The new synthetic technology was applied to the synthesis of nocathiacin I ( 1) model systems ( 2 and 3a– c) containing the N-hydroxyindole structural motif.

Palladium-Catalysed Cross-Coupling Reactions on Pyridazine Moieties

This Account focuses on the palladium-catalysed cross-coupling reactions of pyridazines. The pyridazine moiety is of significant importance in the pharmaceutical as well as the agrochemical field. Synthetic transformations on this moiety, to yield several diverse analogues for a wide array of applications, have received a considerable boost with the advent of palladium-catalysed cross-coupling reactions. These reactions facilitate the direct introduction of suitable groups on the pyridazine nucleus via carbon-carbon or carbon-heteroatom bond formations. This Account presents a brief account of the inherent advantages of palladium chemistry on this moiety followed by seminal work and subsequent developments on this topic.

Rhodium(II)-Catalyzed Reaction of Diazocompounds in the Service of Organic Synthesis of Natural and Non-Natural Products

The rhodium(II)-carbenoid mediated transformation of diazocarbonyl compounds is well recognized as a useful process for the facile formation of carbon-carbon and carbon-heteroatom bonds under mild reaction conditions. In this review, the incorporation of rhodium(II)-carbenoid transformations in the synthetic planning and the eventual application of rhodium(II) carbenoid reactions in the synthesis of natural products, non-natural compounds of medicinal importance, and advanced intermediates are discussed. Focus is placed on the use of intermolecular and intramolecular C-H and X-H insertion, intermolecular and intramolecular cyclopropanation, and tandem ylide (carbonyl, ammonium, oxonium, sulfonium) formation/1,3-dipolar cycloaddition, [2,3]-sigmatropic or Stevens [1,2]-rearrangement reactions as key step(s) in the synthetic routes. Keywords: Rhodium-carbenoid, insertion, cyclopropanation, ylide, enantioselective, diastereoselective, synthesis, metallocarbene

Iridium-Catalyzed Formation of Carbon-Carbon and Carbon-Heteroatom Bonds

The progress in catalytic organic synthesis with iridium was far behind that with rhodium or palladium in the early 1990s. However, many useful reactions have recently been reported, and iridium catalysts have now been recognized to be useful in organic synthesis. This review covers iridium-catalyzed carbon-carbon and carbon-heteroatom bond formation with particular emphasis on useful reactions for organic synthesis.

Transition Metal Catalyzed Reactions of Carbon—Heteroatom Bond Formation by Substitution and Addition Processes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Microwaves in organic and medicinal chemistry

Preface. Personal Foreword. 1. Introduction: Microwave Synthesis in Perspective. 1.1 Microwave Synthesis and Medicinal Chemistry. 1.2 Microwave: Assisted Organic Synthesis (MAOS) - A Brief History. 1.3 Scope and Organization of the Book. 2. Microwave Theory. 2.1 Microwave Radiation. 2.2 Microwave Dielectric Heating. 2.3 Dielectric Properties. 2.4 Microwave Versus Conventional Thermal Heating. 2.5 Microwave Effects. 2.5.1 Thermal Effects (Kinetics). 2.5.2 Specific Microwave Effects. 2.5.3 Non-Thermal (Athermal) Microwave Effects. 3. Equipment Review. 3.1 Introduction. 3.2 Domestic Microwave Ovens. 3.3 Dedicated Microwave Reactors for Organic Synthesis. 3.4 Multimode Instruments. 3.4.1 Milestone s.r.1. 3.4.2 CEM Corporation. 3.4.3 Biotage AB. 3.4.4 Anton Paar GmbH. 3.5 Single-Model Instruments. 3.5.1 Biotage AB. 3.5.2 CEM Corporation. 3.6 Discussion. 4. Microwave Processing Techniques. 4.1 Solvent-Free Reactions. 4.2 Phase-Transfer Catalysis. 4.3 Reactions Using Solvents. 4.3.1 Open-versus Closed-Vessel Conditions. 4.3.2 Pre-Pressurized Reaction Vessels. 4.3.3 Non-Classical Solvents. 4.4 Parallel Processing. 4.5 Scale-Up in Batch and Continuous-Flow. 5. Starting with Microwave Chemistry. 5.1 Why Use Microwave Reactors? 5.2 Translating Conventionally Heated Methods. 5.2.1 Open and Closed Vessels? 5.2.2 Choice of Solvent. 5.2.3 Temperature and Time. 5.2.4 Microwave Instrument Software. 5.3 Reaction Optimization and Library Generation - A Case Study. 5.3.1 Choice of Solvent. 5.3.2 Catalyst Selection. 5.3.3 Time and Temperature. 5.3.4 Reinvestigation by a Design of Experiments Approach. 5.3.5 Optimization for Troublesome Building Block Combinations. 5.3.6 Automated Sequential Library Production. 5.4 Limitations and Safety Aspects. 6. Literature Survey Part A: General Organic Synthesis. 6.1 Transition Metal-Catalyzed Carbon-Carbon Bond Formations. 6.1.1 Heck Reactions. 6.1.2 Suzuki Reactions. 6.1.3 Sonogashira Reactions. 6.1.4 Stille Reactions. 6.1.5 Negishi, Kumada, and Related Reactions. 6.1.6 Carbonylation Reactions. 6.1.7 Asymmetric Allylic Alkyations. 6.1.8 Miscellaneous Carbon-Carbon Bond-Forming Reactions. 6.2 Transition Metal-Catalyzed Carbon-Heteroatom Bond Formations. 6.2.1 Buchwald-Hartwig Reactions. 6.2.2 Ullmann Condensation Reactions. 6.2.3 Miscellaneous Carbon-Heteroatom Bond-Forming Reactions. 6.3 Other Transition Metal-Mediated Processes. 6.3.1 Ring Closing Metathesis. 6.3.2 Pauson-Khand Reactions. 6.3.3 Carbon-Hydrogen Bond Activation. 6.3.4 Miscellaneous Reactions. 6.4 Rearrangement Reactions. 6.4.1 Claisen Rearrangements. 6.4.2 Domino/Tandem Claisen Rearrangements. 6.4.3 Squaric Acid-Vinylketene Rearrangements. 6.4.4 Vinylcyclobutane-Cyclohexene Rearrangements. 6.4.5 Miscellaneous Rearrangements. 6.5 Diels-Alder Cycloaddition Reactions. 6.6 Oxidations. 6.7 Catalytic Transfer Hydrogenations. 6.8 Mitsunobu Reactions. 6.9 Glycosylation Reactions and Related Carbohydrate-Based Transformations. 6.10 Multicomponent Reactions. 6.11 Alkylation Reactions. 6.12 Nucleophilic Aromatic Substitutions. 6.13 Ring-Opening Reactions. 6.13.1 Cyclopropane Ring-Opening. 6.13.2 Aziridine Ring-Openings. 6.13.3 Epoxide Ring-Opening. 6.14 Addition and Elimination Reactions. 6.14.1 Michael Additions. 6.14.2 Addition to Alkenes. 6.14.3 Addition to Alkenes. 6.14.4 Addition to Nitriles. 6.15 Substitution Reactions. 6.16 Enamine and Imine Formations. 6.17 Reductive Aminations. 6.18 Ester and Amide Formation. 6.19 Decarboxylation Reactions. 6.20 Free Radical Reactions. 6.21 Protection/Deprotection Chemistry. 6.22 Preparation of Isotopically Labeled Compounds. 6.23 Miscellaneous Transformations. 6.24 Heterocycle Synthesis. 6.24.1 Three-Membered Heterocycles with One Heteroaton. 6.24.2 Four-Membered Heterocycles with One Heteroatom. 6.24.3 Five-Membered Heterocycles with One Heteroatom. 6.24.4 Five-Membered Heterocycles with Two Heteroatom. 6.24.5 Five-Membered Heterocycles with Three Heteroatom. 6.24.6 Five-Membered Heterocycles with Four Heteroatom. 6.24.7 Six-Membered Heterocycles with One Heteroatom. 6.24.8 Six-Membered Heterocycles with Two Heteroatom. 6.24.9 Six-Membered Heterocycles with Three Heteroatom. 6.24.10 Larger Heterocyclic and Polycyclic Ring Systems. 7. Literature Survey Part B: Combinatorial Chemistry and High-Throughput Organic Synthesis. 7.1 Solid-Phase Organic Synthesis. 7.1.1 Combinatorial Chemistry and Solid-Phase Organic Synthesis. 7.1.2 Microwave Chemistry and Solid-Phase Organic Synthesis. 7.1.3 Peptide Synthesis and Related Examples. 7.1.4 Resin Functionalization. 7.1.5 Transition Metal Catalysis. 7.1.6 Substitution Reactions. 7.1.7 Multicomponent Chemistry. 7.1.8 Microwave-Assisted Condensation Reactions. 7.1.9 Rearrangements. 7.1.10 Cleavage Reactions. 7.1.11 Miscellaneous. 7.2 Soluble Polymer-Supported Synthesis. 7.3 Fluorous Phase Organic Synthesis. 7.4 Grafted Ionic Liquid-Phase-Supported Synthesis. 7.5 Polymer-Supported Reagents. 7.6 Polymer-Supported Catalysts. 7.6.1 Catalysts on Polymeric Supports. 7.6.2 Silica-Grafted Catalysts. 7.6.3 Catalysts Immobilized on Glass. 7.6.4 Catalysts Immobilized on Carbon. 7.6.5 Miscellaneous. 7.7 Polymer-Supported Scavengers. 8. Outlook and Conclusions. Index.