Pyridine-copper catalyst

Evans DA, Barnes DM, Johnson JS, Lectka T, von Matt P, Miller SJ, Murry JA, Norcross RD, Shaughnessy EA, Campos KR (1999) Bis(oxazoline) and bis(oxazolinyl)pyridine copper complexes as enantioselective Diels-Alder catalysts reaction scope and synthetic applications. J Am Chem Soc 121 7582-7594... 

Decomposition of aryl diazonium salts. Cuprous oxide (1, 169-170) has been the catalyst of choice for homolytic decomposition of aryl diazonium salts.2 It has the disadvantage of being effective only in an acidic medium. Lewin and Michl3 have examined the effectiveness of various copper(I) perchlorates complexed with heterocyclic amines. Of the various copper(I) salts, tetrakis(pyridine)copper(l) perchlorate is... 

The synthesis of arsonium ylides 384 from diazocyclopentadienes 383 and tri-phenylarsine has been reexamined with respect to the efficiency of various copper-containing catalysts Whereas copper bronze gave only ca. 55 % of ylide, yields over 80% were provided by the use of Ou(II) complexes of p-diketonates derived from acetylacetone, 3-methylacetylacetone, benzoylacetone or dibenzoylmethane, as well as by bis[4-(phenylimino)-2-pentanonato-N,0-]copper(II) and Cu(II) acetate, all used in boiling benzene. The sterically more demanding complex bis(dipivaloyl-methanato)copper(II) as well as dichlorodipyridinecopper(II) proved less efficient. CopperfTI) tartrate, the dibenzo-14-crown 6/copper complex and furthermore the acetylacetonate complexes of Co, Ni, Pt and Zn were totally ineffective. When 383a was decomposed by Cu(acac)2 in the presence of pyridine or thioanisole. 

A novel soluble complex, (r/2-ethene)hydrotris(3,5-dimethylpyrazol-l-yl)boratocopper(I) (3) mediates the cyclopropanation of styrene, hex-1 -ene, and cyclooctene with ethyl diazoacetate in 76-96% yield (25 °C, 1 mol% of catalyst).153 Copper complexes with the tridentate 2,6-bis[(5-oxo-2,5-dihydropyrrol-2-ylidene)methyl]pyridine ligand or homologous tetradentate 1,1 -bipyridine and l,l -biisoquinoline ligands are also suited to cyclopropanation of styrene with ethyl diazoacetate.1533... 

Heterocyclic Compounds. Such materials undergo catalytic hydrogenation to yield the corresponding saturated derivatives. Thus, pyrrole is slowly converted to pyrrolidine at 200 C over either a nickel or copper-chromium oxide catalyst pyridine and pyridine derivatives behave similarly. Compounds such as furan and dihydropyran reduce rapidly and behave more like olefins in reactivity. Similarly, thiophene is converted to the tetrahydro derivative. 

Preparation of a 0.025-M solution of (5,5 )-bis(phenyloxazo> linyl)pyridine copper (H) hexafluoroantimonate (87, Scheme 10.20) Dichloromethane (10 mL) was added to a mixture of (S,S)-bis(phenyloxazolinyl)pyridine (92 mg, 0.25 mmol), CuCL (34 mg, 0.25 mmol), and AgSbFe (172 mg, 0.50 mmol) in N2 atmosphere. The resulting mixture was vigorously stirred for 4 hours and filtered through a plug of cotton. The resulting clear blue liquid was used as a 0.025-M solution of catalyst 87. This solution could be kept at ambient temperature for one week without any loss of activity or precipitation. 

R often Me) formed by oxidative polymerization of phenols using oxygen with copper and an amine (pyridine) as catalysts. The products are thermoplastics used in engineering applications and in electrical equipment. 

CO, and methanol react in the first step in the presence of cobalt carbonyl catalyst and pyridine [110-86-1] to produce methyl pentenoates. A similar second step, but at lower pressure and higher temperature with rhodium catalyst, produces dimethyl adipate [627-93-0]. This is then hydrolyzed to give adipic acid and methanol (135), which is recovered for recycle. Many variations to this basic process exist. Examples are ARCO s palladium/copper-catalyzed oxycarbonylation process (136—138), and Monsanto s palladium and quinone [106-51-4] process, which uses oxygen to reoxidize the by-product... 

In addition to the Raney nickel catalysts, Raney catalysts derived from iron, cobalt, and copper have been examined for their action on pyridine. At the boiling point of pyridine, degassed Raney iron gave only a very small yield of 2,2 -bipyridine but the activity of iron in this reaction is doubtful as the catalyst was subsequently found to contain 1.44% of nickel. Traces of 2,2 -bipyridine (detected spectroscopically) were formed from pyridine and a degassed, Raney cobalt catalyst but several Raney copper catalysts failed to produce detectable quantities of 2,2 -bipyridine following heating with pyridine. 

Evans et al. reported that the his(oxazolinyl)pyridine (pybox) complex of copper(II) 17 is a selective catalyst of Diels-Alder reactions between a-bromoacrolein or methacrolein and cydopentadiene affording the adducts in high enantioselectivity [23] (Scheme 1.30). Selection of the counter-ion is important to achieve a satisfactory reaction rate and enantioselectivity, and [Cu(pyhox)](ShFg)2 gave the best result. This catalyst is also effective for the Diels-Alder reaction of acrylate dieno-philes (vide infra). 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Associated to copper(II) pre-catalysts, bis(oxazolines) also allowed the asymmetric Diels-Alder and hetero Diels-Alder transformations to be achieved in nearly quantitative yield and high diastereo- and enantioselectivities. Optically active sulfoximines, with their nitrogen-coordinating site located at close proximity to the stereogenic sulfur atom, have also proven their efficiency as copper ligands for these asymmetric cycloadditions. Other precursors for this Lewis acid-catalyzed transformation have been described (e.g., zinc salts, ruthenium derivatives, or rare earth complexes) which, when associated to bis(oxazolines), pyridine-oxazolines or pyridine-bis(oxazolines), led to efficient catalysts. 

Ghosh et al. [70] reviewed a few years ago the utihty of C2-symmetric chiral bis(oxazoline)-metal complexes for catalytic asymmetric synthesis, and they reserved an important place for Diels-Alder and related transformations. Bis(oxazoline) copper(II)triflate derivatives have been indeed described by Evans et al. as effective catalysts for the asymmetric Diels-Alder reaction [71]. The bis(oxazoline) Ugand 54 allowed the Diels-Alder transformation of two-point binding N-acylimide dienophiles with good yields, good diastereos-electivities (in favor of the endo diastereoisomer) and excellent ee values (up to 99%) [72]. These substrates represent the standard test for new catalysts development. To widen the use of Lewis acidic chiral Cu(ll) complexes, Evans et al. prepared and tested bis(oxazoHnyl)pyridine (PyBOx, structure 55, Scheme 26) as ligand [73]. 

Thioacetals eliminate to vinylsulfides in the presence of CuOTf (Scheme 46).192 Cu1 and Cu11 triflates are mild Lewis acids for Friedel-Crafts acylation and alkylation reactions. CuOTf effectively catalyzes the reaction of anisole with selenoesters.193,194 Copper(II) sulfate promotes epoxide ring opening reactions in the presence of pyridine,195 with retention of configuration being observed. Cu(OTf)2 is a catalyst for the ring opening of aziridine by aniline.196... 

The solvent process involves treating phthalonitrile with any one of a number of copper salts in the presence of a solvent at 120 to 220°C [10]. Copper(I)chloride is most important. The list of suitable solvents is headed by those with a boiling point above 180°C, such as trichlorobenzene, nitrobenzene, naphthalene, and kerosene. A metallic catalyst such as molybdenum oxide or ammonium molybdate may be added to enhance the yield, to shorten the reaction time, and to reduce the necessary temperature. Other suitable catalysts are carbonyl compounds of molybdenum, titanium, or iron. The process may be accelerated by adding ammonia, urea, or tertiary organic bases such as pyridine or quinoline. As a result of improved temperature maintenance and better reaction control, the solvent method affords yields of 95% and more, even on a commercial scale. There is a certain disadvantage to the fact that the solvent reaction requires considerably more time than dry methods. 

The basic study was performed on copper complexes with N,N,N, N1-tetramethylethane-1,2-diamine (TMED), which were known to be very effective oxidative coupling catalysts (7,12). From our first kinetic studies it appeared that binuclear copper complexes are the active species as in some copper-containing enzymes. By applying the very strongly chelating TMED we were able to isolate crystals of the catalyst and to determine its structure by X-ray diffraction (13). Figure 1 shows this structure for the TMED complex of basic copper chloride Cu(0H)Cl prepared from CuCl by oxidation in moist pyridine. 

So, both effects maintain an enlarged local concentration of active catalytic centers and cause the rate of oxidative coupling with polymeric catalysts to be higher than with equivalent amounts of low molecular weight analogs, especially for low 1igand/copper ratios. This rate enhancement is clearly demonstrated in Figure 5 for polydentates (I) vs. DMBA (J 7), and was also found for polydentate (II) vs. pyridine (18). 

The refered oxidative polymerization of phenols with the copper-pyridine catalyst was carried out as in lit. (7,8). 

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