Copper enolates structure

Activation of C=N double bonds by copper Lewis acids for nucleophilic addition has also been reported (Sch. 37) [73]. The a-imino ester 157 undergoes alkylation at the imine carbon with a variety of nucleophiles when catalyzed by copper Lewis acids. The presence of the electron-withdrawing ester group increases the reactivity of the imine and also assists in the formation of a stable five-membered chelate with the Lewis acid. Evidence for Cu(I) Lewis-acid catalysis and a tetrahedral chelate was obtained by FTIR spectroscopy, from the crystal structure of the catalyst, and from several control experiments. The authors rule out the intermediacy of a copper enol-ate in these transformations. The asymmetric alkylation of A,0-acetals with enol silanes mediated by a copper Lewis acid proceeding with high selectivity has been reported [74],... 

Ricci and coworkers [64] studied oxazoline moiety fused with a cyclopenta[P]thio-phene as ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone. The structure of the active Cu species was determined by ESI-MS. Evans and coworkers [65] studied C2-symmetric copper(II) complexes as chiral Lewis acids. The catalyst-substrate species were probed using electrospray ionization mass spectrometry. Comelles and coworkers studied Cu(II)-catalyzed Michael additions of P-dicarbonyl compounds to 2-butenone in neutral media [66]. ESI-MS studies suggested that copper enolates of the a-dicarbonyl formed in situ are the active nucleophilic species. Schwarz and coworkers investigated by ESI-MS iron enolates formed in solutions of iron(III) salts and [3-ketoesters [67]. Studying the mechanism of palladium complex-catalyzed enantioselective Mannich-type reactions, Fujii and coworkers characterized a novel binuclear palladium enolate complex as intermediate by ESI-MS [68]. 

Despite the key role that has been attributed to copper enolates as postulated intermediates in additions to enones [78], structural information is very rare for enolates of copper as well as the higher elements in group 11. A recent crystal structure of a copper(I) ester enolate 46, which functions as a relevant intermediate in catalytic enolate arylation reactions, features a cationic Cu(I) center coordinated to two phenanthroline ligands and a free unligated enolate anion (Figure 3.13) [79]. A gold(I) enolate of acetophenone is a C-bound tautomer, as expected by the low oxophilic character of the noble metal and confirmed by a crystal structure analysis [80]. 

The authors assumed that the catalytically active species might be a copper(I) complex originating from reduction by the silyl dienolate 214. As a consequence, the aldol reaction was performed with the chiral copper(I) complex [Cu(OfBu)-(S)-270], and identical results in terms of the stereochemical outcome were obtained. In addition, the reaction was followed by react IR. The study led to evidence of a copper(I) enolate as the active nucleophile, and the catalytic cycle also shown in Scheme 5.77 was proposed. The reaction of the copper(I) complex Cu(OiBu)-(S)-270 with silyl dienolate 214 represents the entry into the catalytic cycle. Under release of trimethylsilyl triflate, the copper enolate 272 forms, whose existence is indicated by in situ IR spectroscopy. Its exact structure remains unclear, but the description as O-bound tautomer is plausible. Upon reaction with the aldehyde, the copper aldolate 273 is generated, which is then silylated by means of the silyl dienol ether 214 to give the (isolable) silylated alcohol 274 from which the aldol product 271 is liberated during the acidic workup [132b]. 

Pyrrolidinyl Enolate-, and Semicorrinate Anions as Chelate Ligands for fron(II) and Copper(II) Ions From Molecular to Collective Structures. 152... 

Reaction of tetrazolyl enole 45 with copper(II) acetate yields the 3D-coordination polymer [ CulL19)21 (46), the structure of which is unequivocally established by single-crystal X-ray diffraction. The formation of 46 is understandable if the enolate of 45 is considered as tridentate chelate ligand and if the intermediate formation of the coordinatively unsaturated self-complimentary copper(II) building block 47 is assumed. The monomers 47 are bidentate coordinating by the two CN donors, which leads to linking of monomers and to coordinative saturation at the copper(II) center of 47 with formation of three-dimensional 0 [Cu(L19)2] (46) (Scheme 17, Fig. 18) [163, 164],... 

Pale yellow cerium dioxide (ceria, ceric oxide) has the fluorite structure and is used in catalysis" ", solid oxide fuel cells (SOFC)", thin film optical waveguides" , reversible oxygen storage materials for automobile catalysts" and for doping copper oxide superconductors". The diverse cerium enolate precursors and deposition methods used in the formation of cerium oxide thin films are summarized in Table 6, whereby the most common precursor for ceria is Ce(thd)4. 

Tetranortriterpenoids.—The structure of sendanin (72), from the bark of a Japanese variety of Melia azedarach, has been confirmed by AT-ray analysis. The novel enol-ether (73) has been isolated from the heartwood of Khaya anthotheca along with 11/3- and lla-acetoxyazadirone (74) and (75). Zinc-copper couple is a very convenient reagent for reduction of epoxides, a,/S-epoxy-lactones, a/S-unsaturated ketones, and a-ketols. The full details of the X-ray analysis of prieurianin have appeared. " ... 

Enantioselection can be controlled much more effectively with the appropriate chiral copper, rhodium, and cobalt catalyst.The first major breakthrough in this area was achieved by copper complexes with chiral salicylaldimine ligands that were obtained from salicylaldehyde and amino alcohols derived from a-amino acids (Aratani catalysts ). With bulky diazo esters, both the diastereoselectivity (transicis ratio) and the enantioselectivity can be increased. These facts have been used, inter alia, for the diastereo- and enantioselective synthesis of chrysan-themic and permethrinic acids which are components of pyrethroid insecticides (Table 10). 0-Trimethylsilyl enols can also be cyclopropanated enantioselectively with alkyl diazoacetates in the presence of Aratani catalysts. In detailed studies,the influence of various parameters, such as metal ligands in the catalyst, catalyst concentration, solvent, and alkene structure, on the enantioselectivity has been recorded. Enantiomeric excesses of up to 88% were obtained with catalyst 7 (R = Bz = 2-MeOCgH4). 

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