Copper-pyridine reagents

Copper-zinc reagents add to various pyridinium salts leading either to the 1,2- or to the L4-adduct, depending on the substituent pattern of the pyridine ring (Scheme 95) 2 . ... 

Copper (II) sulphate-pyridine reagent When a neutral solution of a thiocyanate is added to a dilute solution of a copper salt containing a few drops of pyridine, a yellowish-green precipitate of the composition [Cu(C5H5N)2](SCN)2 is formed the compound is soluble in chloroform to which it imparts an emerald-green colouration. Cyanates interfere with this reaction excess of pyridine should be avoided. 

Copper(II) reagents for the conversion of catechols and o-benzoquinones to muconic acid monoesters can also be prepared by adding a nucleophile ROH (R = Me, Et, n-Pr, etc. ) to the products of oxidation of CuCl in pyridine [40],... 

The methoxy(pyridine)copper(II) reagent 27 reacts with 4-t-butylcatechol and its derivatives (30) in the absence of dioxygen, under anhydrous conditions [53] the most probable pathway involves the corresponding o-benzoquinone as an intermediate en route to 31 and via acid hydrolysis 32 ... 

Poly(2-vinylpyridine), with Mv=36,000, was purchased from Aldrich Chemical Co. and purified by two precipitations from ethanol into deionized water. CuC12-2H20 (ACS purity) and poly(4-vinylpyridine) from Mallinckrodt and Polysciences Inc. respectively, were used as received. Complexes with different ratios of Cu to pyridine moiety were formed in solution (95% methanol, 5%H20). Due to decreasing solubility of the complex with increasing copper concentration, the concentration of reagents was varied as shown in Table I. 

Low chemical yields and a-selectivity on the allyl copper reagent are observed with the phenylthio analogues. These observations suggest that the pyridine nitrogen facilitates transmetalation and or cuprate reactivity and plays a role in the regio-selectivity of the reaction. 

In the solid state, the metal atoms in bis(salicylaIdoximato)copper(II) show two additional contacts with the oxime oxygens of adjacent molecules, resulting in a distorted octahedral structure. However, the axial Cu—O distance (2.66 A) is much longer than the metal—ligand distances in the square-planar array (Cu—O, 1.92 A and Cu—N, 1.94 A).154 Studies by ESR of copper(II) extracts of the commercial reagent SME 529 (14 R = Me, R = C9H)9) have shown that the copper complex exists as a square-planar species in hydrocarbon solutions, but that five-coordinate adducts are formed in the presence of ammonia or pyridine.155... 

The combinations of chlorotrimethylsilane-hexamethylphosphoramide (HMPA) or chlorotrimethylsi-lane-4-(dimethylamino)pyridine (DMAP) are also powerful accelerants for copper(I)-catalyzed Grignard conjugate additions,33 and stoichiometric organocopper and homocuprate additions (Scheme 21 ).36 However, these reactions must be performed in tetrahydrofuran instead of ether.37 These procedures are noted for their high yields with stoichiometric quantities of Grignard reagents, excellent chemoselectivity and efficiency with a,3-unsaturated amides and esters and enals.58 Typically, additions to enals proceed via the S-trans conformers to afford stereo-defined silyl enol ethers for example, enals (122) and (124) give the ( )-silyl enol ether (123) and (Z)-silyl enol ether (125), respectively. 

Sulfuric acid, concentrated and dilute Silver nitrate Copper sulfate-pyridine test Cyanates, OCN Vigorous effervescence, due largely to evolution of carbon dioxide, with concentrated acid producing a more dramatic effect Curdy white precipitate of silver cyanate Lilac-blue precipitate (interference by thiocyanates) reagent is prepared by adding 2 or 3 drops of pyridine to 0.25 M CuS04 solution... 

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