SYNTHESIS with copper complexes

Arylbenzoxazoles have been prepared in moderate yields by allowing aromatic aldehydes to react with copper complexes of o-nitrosophenols (Scheme 108).172 The role of the copper in reactions of this type is unclear but it may be noted that the uncomplexed nitrosophenols are relatively labile.173 Copper complexes of o-nitrosophenols have also been used for the synthesis of benzoxazines (see Section V,D). 

Reactions of Dioxvgen with Copper Complexes - Reversible Binding While there has been a great deal of effort and success in the synthesis and... 

Subsequent investigations revealed that the corresponding hexafluoroanti-monate complex 166 generally possessed higher reactivity and resulted in improved stereoselectivity in such cycloadditions [89]. In all cases, the observed induction could be explained in terms of a catalyst-substrate model complex as depicted for 163 with a distorted tetrahedral geometry around the copper(II) center. The tert-butyl substituents on the C2-symmetric chiral ligand efficiently shield one of the r-faces of the chelated dienophiles [90, 91]. A variety of substrates readily participate in enantioselective Diels-Alder reactions with copper complex 166. An intramolecular variant of such cycloadditions furnished 167 (96% ee, dr >99 1) and constituted a key step in the synthesis of the marine natural product (-)-isopulo upone... 

Available information on the mechanism of cyclocondensation is rather contradictory. According to one hypothesis, both the condensation of aryl halides with copper acetylides and the cyclization occur in the same copper complex (63JOC2163 63JOC3313). An alternative two-stage reaction route has also been considered condensation followed by cyclization (66JOC4071 69JA6464). However, there is no clear evidence for this assumption in the literature and information on the reaction of acetylenyl-substituted acids in conditions of acetylide synthesis is absent. 

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

Scheme 10 Synthesis of copper and zinc polysulfido complexes by the reaction of a metal with Sg in donor solvents...

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). 

Synthesis of complex 1. The pentadentate salen catalyst 1 was synthesized as described (9). In short, the tosylated 2-[2-(2-methoxyethoxy)-ethoxy]-ethanol 2 (10) was reacted with 2,4-dihydroxybenzaldehyde 3 to yield 4-alkoxy salicylaldehyde 4 after chromatographic purification (eq. 1). Subsequent condensation of 4 with 1,3-diaminopropanol yielded water-soluble salen ligand 5 in sufficient purity and 89% yield (11). The formation of an azomethine bond is indicated by a shift of the NMR signal for the carbonyl carbon from 194.4 ppm in aldehyde 4 to 166.4 ppm for the imino carbon in 5. The pentadentate ligand 5 was then treated with copper(ll) acetate in methanol to obtain the dinuclear copper(ll) complex 1 as a green solid (eq. 2) (11). 

ARGET ATRP has been successfully applied for polymerization of methyl methacrylate, ft-butyl acrylate and styrene in the presence of Sn(EH)2 (10 mol% vs. alkyl halide initiator or 0.07 mol% vs. monomer) [164,165]. For all monomers, polymerizations were well controlled using between 10 and 50 ppm of copper complexes with highly active TPMA and Me6TREN ligands. ARGET ATRP has also been utilized in the synthesis of block copolymers (poly(n-butyl acrylate)— -polystyrene and polystyrene-Z -poly(n-butyl acrylate) [164,165] and grafting... 

The copper complex of these bis(oxazoline) compounds can also be used for hetero Diels-Alder reactions of acyl phosphonates with enol ethers.43 5 A favorable acyl phosphonate-catalyst association is achieved via complexation between the vicinal C=0 and P=0 functional groups. The acyl phosphonates are activated, leading to facile cycloaddition with electron-rich alkenes such as enol ethers. The product cyclic enol phosphonates can be used as building blocks in the asymmetric synthesis of complicated molecules. Scheme 5-36 shows the results of such reactions. 

Recent Advance of Asymmetric Synthesis of (1R)-tr sms-Chrysanthemic Acid with a New Chiral Copper Complex... 

Asymmetric synthesis of 2,5-dimethyl-2,4-hexadiene (28) and /-menthyl diazoacetate (29) with chiral copper complexes (30) was successfully conducted by Aratani et al. [13] to afford the (1 A)-chrysanthem ic acid /-menthyl ester (31) in high optical and chemical yield. Since this finding, a lot of chiral copper complexes have been reported and applied to the asymmetric synthesis of (IR)-chrysanthemate. However, these copper complexes required more than 1 mol% of the catalyst and the cis/trans ratio still remains unsatisfactory. Moreover, /-menthyl ester was crucial for the high enantioselectivity. Given an industrial production of... 

Three major approaches have been followed to provide reactive dyes in this important sector. One category is closely related to the reddish blue monoazo 1 1 copper complexes already described (section 7.5.8). To provide the higher substantivity and deeper intensity for build-up to navy blue shades, a second unmetallised azo grouping is introduced. As with the brown dyes, the A—>M—>E pattern is adopted for their synthesis. Component A is normally a sulphonated aniline, M an aminophenol or aminocresol and E a sulphonated naphthol or aminonaphthol. The reactive system (Z) is usually, but not invariably, located on the E component and the copper atom always coordinates with an o,o -dihydroxyazo grouping provided by the M and E components (7.109). 

Synthesis and Characterization of N-[l,10-Phenanthroline]-N -[(Benzo-15-Crown-5)yl] Thionrea and Its Complex with Copper(I)... 

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