Carbonylation copper complexes

Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

The use of chiral bis(oxazoline) copper catalysts has also been often reported as an efficient and economic way to perform asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imines with conjugated dienes [81], with the main focus on the application of this methodology towards the preparation of biologically valuable synthons [82]. Only some representative examples are listed below. For example, the copper complex 54 (Scheme 26) has been successfully involved in the catalytic hetero Diels-Alder reaction of a substituted cyclohexadiene with ethyl glyoxylate [83], a key step in the total synthesis of (i )-dihydroactinidiolide (Scheme 30). 

Carbonyl- and imino-ene reactions were also catalyzed by the bis(oxazo-line)-copper complexes of ligands 6a, 6b and 11b supported on zeoHte Y (Scheme 13) [69]. The enantioselectivities obtained with the supported catalysts were similar or better than those obtained in homogeneous phase with the same ligands. Some relevant examples are shown in Table 12. 

The required long planar shape is more readily supplied by simple disazo structures such as Cl Direct Blue 1 (4.60). Copper complexes of such disazo compounds are important and are dealt with elsewhere (section 5.5.3). A widely used method of producing A—A type disazo dyes relies on treating J acid with phosgene (COCl2) to give the bis-coupling component carbonyl J acid (4.61). 

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],... 

A group at the Academy of Sciences in Moscow 197) has synthesized chiral threonine. Derivatives of cyclic imino acids form copper complexes with glacine and carbonyl compounds. Hydroxyethylation with acetaldehyde and decomposition of the resulting complexes produced threonine with an optical purity of up to 97-100% and with threo/allo ratios of up to 19 1 197). The chiral reagents could be recovered and re-used without loss of stereoselectivity. The mechanism of this asymmetric synthesis of amino acids via glacine Schiff base/metal complexes was also discussed 197). 

Another chiral aldehyde suitable for such transformations is the recently prepared pyridoxal derivative (121).323 Even more recent examples of chiral carbonyl compounds (122) have been used for the partial resolution of amino acids. The enantiomers of compounds (122) undergo reaction with racemic a-amino acids and copper(II) ions to give preferential formation of enantiomeric copper complexes. The ( -enantiomers of (122) preferentially form complexes containing the... 

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... 

The mechanism of the enantioselective 1,4-addition of Grignard reagents to a,j3-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines has been explored through kinetic, spectroscopic, and electrochemical analysis.86 On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. 

Although transesterification and transamidation reactions of simple carbonyl ligands are usually associated with the involvement of a co-ordinated nucleophile, there are some well-documented processes which unambiguously involve attack by an external nucleophile upon a co-ordinated electrophile. Dithiocarbamate complexes contain a chelated. S, 5"-bonded dithioamide ligand and undergo facile transamination reactions upon treatment of the copper complexes with amines (Fig. 3-22). 

Mannam S, Alamsetti SK, Sekar G (2007) Aerobic, chemoselective oxidation of alcohols to carbonyl compounds catalyzed by a DABCO-copper complex under mild conditions. Adv Synth Catal 349(14-15) 2253-2258... 

Moreover, we believe that the azo form helps in stabilizing several of the reactive copper complexes involved in this catalytic cycle such as the hydroxy copper complex 17. Thus, we surmise that this novel catalytic, aerobic oxidation procedure for alcohols into carbonyl derivatives proceeds via a dehydrogenation mechanism and relies on the effective role of hydrazine or azo compounds as hydrogen shuttles and stabilizing ligands for the various copper complexes (20). 

Stoichiometric amounts of substituted azo-compounds have been used to oxidize magnesium alkoxides to the corresponding carbonyl compounds Narasaka, K. Morikawa, A. Saigo, K. Mukaiyama, T. Bull. Chem. Soc. Jpn. 1977, 50, 2773 The decomposition mechanism of hydrazines in the presence of copper-complexes has been reported (a) Erlenmeyer, H. Flierl, C. Sigel, H. J. Am. Chem. Soc. 1969, 91, 1065 (b) Zhong, Y. Lim, P. K. J. Am. Chem. Soc 1989, 111, 8398. 

More recently, Pfaltz has reported high enantioselectivities for the cyclopropanation of monosubstituted alkenes and dienes with diazo carbonyl compounds using chiral (semicorrinato)copper complexes (P-Cu) (23-25), and Evans, Masamune, and Pfaltz subsequently discovered exceptional enantioselectivities in intermolecular cyclopropanation reactions with the analogous bis-oxazoline copper complexes (26-28). With the exception of the chiral (camphorquinone dioximato)cobalt(II) catalysts (N-Co) reported by Nakamura and coworkers (29,30), whose reactivities and selectivities differ considerably from copper catalysts, chiral complexes of metals other than copper have not exhibited similar promise for high optical yields in cyclopropanation reactions (37). 

Methylene ( CH2) generated photochemically or thermally from diazomethane is highly reactive and is prone to incur side reactions to a substantial extent. In order to avoid these undesirable complexities, the cyclopropanation of multiple bonds with diazomethane has usually been carried out under catalytic conditions The catalysts most frequently employed are copper salts and copper complexes as well as palladium acetate. The intermediate produced in the copper salt-catalyzed reactions behaves as a weak electrophile and exhibits a preference to attack an electron-rich double bond. It is also reactive enough to attack aromatic nuclei. In contrast, the palladium acetate-catalyzed decomposition of diazomethane cyclopropanates a,a- or a,jS-disubstituted a,jS-unsaturated carbonyl compounds in high yields (equation 47). The trisubstituted derivatives, however, do not react. The palladium acetate-catalyzed reaction has been applied also for the cyclopropanations of some strained cyclic alkenesstyrene derivatives and terminal double bondsHowever, the cyclopropanation of non-activated, internal double bonds occurs only with difficulty. The difference, thereby. 

---