The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.

Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3

However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.

Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.

A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

/pdf/aerobic-copper-catalyzed-organic-reactions-3ctljpvivz.pdf

Aerobic Copper-Catalyzed Organic Reactions

Helicenes: synthesis and applications.

2.1.8. Michael Reaction 2245 2.1.9. Others 2247 2.2. Cyclization Reactions 2248 2.2.1. Carbon Diels−Alder Reactions 2248 2.2.2. Aza-Diels−Alder Reactions 2252 2.2.3. Other Hetero-Diels−Alder Reactions 2255 2.2.4. Ionic Diels−Alder Reaction 2256 2.2.5. 1,3-Dipolar Cycloadditions 2256 2.2.6. Other Cycloaddition Reactions 2258 2.2.7. Prins-type Cyclization 2259 2.3. Friedel−Crafts Acylation and Alkylation 2259 2.4. Baylis−Hillman Reaction 2263 2.5. Radical Addition 2264 2.6. Heterocycle Synthesis 2267 2.7. Diazocarbonyl Insertion 2270 3. C−X (X ) N, O, P, Etc.) Bond Formation 2271 3.1. Aromatic Nitration and Sulfonylation 2271 3.2. Michael Reaction 2272 3.3. Glycosylation 2273 3.4. Aziridination 2275 3.5. Diazocarbonyl Insertion 2276 3.6. Ring-Opening Reactions 2277 3.7. Other C−X Bond Formations 2280 4. Oxidation and Reduction 2280 4.1. Oxidation 2280 4.2. Reduction 2281 5. Rearrangement 2283 6. Protection and Deprotection 2285 6.1. Protection 2285 6.2. Deprotection 2288 7. Polymerization 2291 8. Miscellaneous Reactions 2291 9. Lanthanide(II) Triflates in Organic Synthesis 2295 10. Conclusion 2295 11. Acknowledgment 2295 12. References 2295

Rare-earth metal triflates in organic synthesis

Digital information processing in molecular systems.

Carbohelicenes belong to a class of fascinating, chiral, and helicoidal molecules, which have a rich history in chemistry since the very beginning of the 20th century. A renewed interest in polyaromatic chemistry and new synthetic challenges toward the search for innovative physical, biological, chemical and opto-electronic properties have brought high motivation in this field of studies. Theoretical insights gained from polyaromatic, chiral, conjugated and distorted π-systems are also responsible for this development. Several synthetic avenues were originally reported for making lower helicenes, but for many years, photochemical synthesis has remained a major method for producing small amount of helicenes. High-dilution conditions is still a limiting factor in their synthesis. The fulgurous impact of organometallic chemistry, novel synthetic methods, and recent catalytic systems has promoted the development of helicene chemistry, toward a library of tailor-made and highly functionalized helicene molecules. Helicene chemistry is being considered as an expanding and modern field, leading to several applications in supramolecular chemistry, in nanosciences, in chemical-biology, in polymers and materials science. This first part of a series of three reviews on carbohelicenes will be devoted to a comprehensive report on non-stereoselective reactions and methods for producing helicenes, along with their functionalization.

One hundred years of helicene chemistry. Part 1: non-stereoselective syntheses of carbohelicenes.

Synthesis of chiral [5]helicenes using aromatic oxy-Cope rearrangement as a key step

Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axle

2-(Bromomethyl)-1-sulfonylaziridines were converted into novel 3-sulfonamido-2,3,4,5-tetrahydro-1,5-benzothiazepines upon treatment with 2-aminothiophenol in THF in the presence of K2CO3. Starting from 3-substituted 2-(sulfonyloxymethyl)aziridines, a regio- and stereocontrolled synthesis of trans-2-phenyl- and trans-4-(phenyl or propyl)-3-sulfonamido-2,3,4,5-tetrahydro-1,5-benzothiazepines was developed in good yields via two different reaction pathways, depending on the nature of the sulfonyloxy group.

Regio- and stereocontrolled synthesis of novel 3-sulfonamido-2,3,4,5-tetrahydro-1,5-benzothiazepines from 2-(bromomethyl)- or 2-(sulfonyloxymethyl)aziridines

Michinori Karikomi

Papers

Synthesis of chiral [5]helicenes using aromatic oxy-Cope rearrangement as a key step

Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axle

Regio- and stereocontrolled synthesis of novel 3-sulfonamido-2,3,4,5-tetrahydro-1,5-benzothiazepines from 2-(bromomethyl)- or 2-(sulfonyloxymethyl)aziridines

Novel synthesis of oxa[9]helicenes by Lawesson’s reagent-mediated cyclization of helical quinone derivatives

A novel synthesis of 3-aminoazetidines by ring transformation of 2-(bromomethyl)aziridines.