Copper salen

Catalyst screening experiments resulted in the discovery that copper(salen) complex 33 was a highly effective catalyst for the conversion of alanine derivative 16b into (f )-a-methyl phenylalanine 17 under the conditions shown in Scheme 8.16. The presence of just 1 mol% of catalyst 33 was sufficient to induce the formation of compound 17 with up to 92% ee and in >70% yield [33]. Allyl bromide, 1-chloromethylnaphthalene and ethyl iodide also reacted with substrate 16b to give the corresponding (H)-a-methyl a-amino acids in the presence of 2 mol % of complex 33 [34], Complex 33 also catalyzed the asymmetric mono-alkylation of glycine-derived substrate 34 by benzylic or allylic halides, to give (H)-a-amino acid derivatives 35 with 77-81% ee. and in greater than 90% yield, as shown in Scheme 8.17. 

Figure 8.2 Gauche- and anti-conformations of a copper(salen) complex.

The X-ray structure of complex 42a [42] showed it to be square planar, and essentially superimposable on the X-ray structure of Cu(salen) complex 33 [45], Complex 42a was found to be catalytically active, and gave (R)-a-methyl-phenylala-nine methyl ester in 83% yield and with 80% ee - results which are essentially identical to those obtained using complex 33. Changing the substrate to compound 38f [which was optimal for the use of copper(salen) complex 33] further increased the enantioselectivity of the reaction to 85%. Experimentally, complex 42a has an advantage compared to copper(salen) complex 33 as it does not require chromatographic purification on Sephadex-LH20 to obtain a pure catalyst. 

COPPER-SALEN COMPLEX AS A PHASE TRANSFER CATALYST... 

CATALYTIC, ASYMMETRIC SYNTHESIS OF o,a-DISUBSTITUTED AMINO ACIDS USING A CHIRAL COPPER-SALEN COMPLEX AS A PHASE TRANSFER CATALYST... 

Fig. 35. Copper-salen catalyzed oxidation of alcohols using H2O2 as the oxidant 105).

Observation of the stereoselective manner of chiral substrates binding to these asymmetric metal-salen complexes was not confined to [VO(l,3)] or chiral epoxides. Recently we showed how asymmetric copper salen complexes, [Cu(l)] and [Cu(4)] (Fig. 1), could also discriminate between chiral amines (R-IS-methylbenzylamine, MBA) as evidenced by multi-frequency CW and pulsed EPR, ENDOR, HYSCORE and DPT [45]. The discrimination of the MBA enantiomers was directly observed by W-band EPR. By simulating the W-band EPR spectra of the individual diastereomeric adduct pairs (i.e. R,R -[Cu(4)]+R-MBA and R,/ -[Cu(4)]-l-5-MBA), accurate spin-Hamiltonian parameters could be extracted for each adduct. The EPR spectmm of the racemic combinations (i.e. ra -[Cu(4)]+rac-MBA) was then simulated using a linear combination of the g/A parameters for the homochiral (R,R -[Cu(4)]+R-MBA) and heterochiral (R,R -[Cu... 

Murphy DM, Caretti I, Carter E et al (2011) Visualising diastereomeric interactions of chiral amine-chiral copper Salen adducts by EPR/ENDOR/HYSCORE spectroscopy and DFT. Inorg Chem (submitted)... 

Abdel Azzem, M., Z.F. Mohamed, and H.M. Fahmy (1995). Electrocatalytic reduction of some imino compounds on a glassy carbon electrode electrochemically modified with a new copper-salen complex. J. Electroanal. Chem. 399,121-125. 

A few Lewis acids have been shown to catalyze the Yonemitsu-type reactions of indoles, aldehydes, and several CH acids (Scheme 13.79). Dimethyhnalonate 358 was successfully reacted with indole 327 and several aldehydes 357 under solvent-free ultrasound irradiation conditions to provide the desired products 359 in moderate yields [135]. Ytterbium triflate was used as the Lewis-acidic catalyst in this case. A copper-salen complex was utilized in water at elevated temperature to facilitate the Yonemitsu-type reaction of indoles 360, aldehydes 361, and malonodinitrile 21 [136]. In close similarity copper(II) acetate was used in polyethylene glycol at elevated temperatures to provide Yonemitsu-type products 366 in moderate to high yields (48-98%) [137]. 

Dadamos TRL, Teixeira MFS (2009) Electrochemical sensor for sulfite determination based on a nanostmctured copper-salen film modified electrode. Electrochim Acta 54 (19) 4552 558. doi 10.1016/j.electacta.2009.03.045... 

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