Carbonyl copper catalysis

The 1,4-addition of Grignard reagents under copper catalysis, followed by a trap of the resulting (magnesium) enolates with an appropriate electrophile, is a versatile method for double functionalization or double carbon-carbon bond formation at the a- and / -positions of an olefinic bond that bears a carbonyl group [Eq. (89)]. Recently, this topic has been extensively reviewed [155]. Examples [170,173,174] of this notion are presented in Eqs. (77), (90) [170], and (91) [174]. 

Treatment of aldehydes with two equivalents of a-bromoketones and Bu Sb produces a,//-unsaturated ketones and debrominated ketones [109], whereas the b.-cal-aly/ed reaction with equimolar amounts of the ketones and It jSb gives -hydroxy-ketones (Scheme 14.45) [110]. The olefination of carbonyl compounds with diazo esters is mediated by BujSb under copper catalysis (Scheme 14.46) [111]. 

In 2005, Fu and co-workers developed an efficient method for the preparation of medium- and large-sized nitrogen heterocycles via copper-catalyzed intramoleeular Af-arylation of phosphoramidates and carbamates. Introduetion of the phosphoryl group or tert-butO q carbonyl at the iV-termini can improve intramolecular cyclization under copper catalysis, and the phosphoiyl (DIPP diisopropylphospho) and tert-butO q carbonyl can easily be removed under the mild conditions (Scheme 4.10). 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

In 2004, Kobayashi et al. introduced enecarbamates as nucleophiles to asymmetric catalysis [48], The addition of enecarbamates to imines in the presence of a chiral copper complex provides access to P-amino imines which can be hydrolyzed to the corresponding p-amino carbonyl compounds [49],... 

The copper(II)-promoted hydrolysis of glycylglycine has been studied in some detail.120 Copper(II) ions catalyze the hydrolysis of glycylglycine in the pH range 3.5 to 6 at 85 °C.120 The pH rate profile has a maximum at pH 4.2, consistent with the view that the catalytically active species in the reaction is the carbonyl-bonded complex. The decrease in rate at higher pH is associated with the formation of a catalytically inactive complex produced by ionization of the peptide hydrogen atom. This view has subsequently been confirmed by other workers,121 in conjunction with an IR investigation of the structures of the copper(II) and zinc(II) complexes in D20 solution.122 Catalysis by cobalt(II),123 and zinc(II), nickel(II) and manganese(II) has also been studied.124-126... 

Somewhat similar effects are seen in the copper(II)-promoted hydrolysis of O-acetyl-2-pyridinecarboxaldoxime (47) (equation 20).215 In this case, water attack and hydroxide ion attack are accelerated by 1.1x10 and 2.2 xlO7 times respectively. Detailed analysis indicates that Cuu-bound water or hydroxide reacts with the carbonyl carbon of the ester as shown in (48). Promotion includes contributions from increases in the effective nucleophile concentration in addition to an enhancement in the leaving group ability. General base catalysis in the attack of coordinated water is also observed. 

The use of transition metal species can lower appreciably the decomposition temperature of ot-diazo-carbonyl compounds they can also alter the reactivity of the carbene intermediate (resulting from the initial nitrogen elimination see Section 3.9.2.1) by complex formation. Hence, the Wolff rearrangement may occur with difficulty or, usually, not at all. Thus, some copper species (excepting, for example, Cul), or Rh and Pd catalysts are inappropriate. Freshly prepared silver(I) oxide has been used most frequently, but silver salts (especially silver benzoate) are sometimes preferred.Silver-based catalysts are usually employed in combination with an alkaline reagent e.g. sodium carbonate or a tertiary amine). Even under silver catalysis competing reactions may be observed, and sometimes the products of Wolff rearrangement may not be obtained (see Section 3.9.2.3). 

Oxidation.—There has been controversy over whether copper is a catalyst for oxidation of hydrocarbons, e.g. cumene over Cu. Allara and Roberts used XPS in their study to examine catalysts for the presence of Cu", Cu ", O ", and OH . t-Butyl hydroperoxide was used as an initiator for their catalytic runs on oxidation of hexadecane. It appears that rin the presence of Cu +0, t-Bu02H produces free radical products which bring about catalysis. In contrast over Cu(OH)2 non-free-radical species are produced with inhibition of reaction. ROOH species were the main products, 40—90 %, with other carbonyls, alcohols, and aldehydes. 

The great majority of intramolecular cyclopropanation reactions of unsaturated a-diazo-carbonyl compounds have been achieved with copper catalysts, especially with copper powder or copper bronze, copper(II) sulfate, and bis(acetylacetonato)copper(II). Homogeneous catalysis by bis(salicylaldimato)copper(II) or copper(I) halide/trialkyl phosphite complexes has repeatedly been reported to be superior to heterogeneous catalysis by other copper(I) and cop-per(II) salts, e.g. formation of and 2. ... 

Scheme 2.7 Selective direct a-fluorination of carbonyl compounds. Copper salt catalysis supposedly acts via formation of the copper enolate complex [19, 20], The formation of the corresponding copper complex of monofluoromalonate, the precursor of difluorinated products, is energetically disfavored.

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