Copper catalysts Henry reaction

The enantioselective Henry reaction by using copper acetate-bis(oxazoline) catalyst is reported by Evans . ... 

Asymmetric Aza-Henry Reactions of Nitronates with Imines. Although the Henry reaction and its aza-analogs are powerful C-C bond-forming reactions, there are few reports of catalytic asymmetric versions of these reactions. The cir-DiPh-Box copper complexes are excellent catalysts for highly diastereo and enantioselective aza-Henry reactions of a variety of trimethyl-silylnitronates with Af-(p-methoxyphenyl)-a-imino-esters (eq 3). The use of an A-(/ -methoxyphenyl) group for protection prevents undesirable side reactions and can be easily removed. The aza-Henry reaction products can be further derivatized to the corresponding a,3-diamino acids whose syntheses have rarely been reported. 

Catalytic enantioselective Henry reactions are known, such as the use of a chiral copper catalyst or a zinc catalyst. The Henry reaction of nitro-methane an a chiral aldehyde under high pressure gives the p-nitro alcohol with excellent enantioselectivity. ... 

Aryl glyoxals, ArCOCHO, or their hydrates, ARCOCH(OH)2, as well as their aliphatic analogues, typically react with nucleophiles at the aldehyde carbon, but a chiral copper(II)-iminopyridine catalyst switches the reactivity, allowing Henry reaction at the ketone, and with high ee, giving a quaternary stereocentre in the product, without any specific protection of the aldehyde. ... 

A syn- and enantio-selective Henry reaction employs copper(II) acetate and a chiral -amino alcohol catalyst. 

Henry Reactions. An enantioselective nitroaldol reaction was catalyzed by a Cu(OAc)2-oxazoline complex. Various aldehydes were treated with nitromethane in the presence of the copper catalyst giving the desired /3-nitroalcohols in good to excellent yields and enantiomeric excesses (eq 32). 

In the very recent past, metal complex catalysis has been used with advantage for the stereo- and enantio selective syntheses based on the Henry and Michael reactions with SENAs (454-458). The characteristic features of these transformations can be exemplified by catalysis of the reactions of SENAs (327) with functionalized imides (328) by ligated trivalent scandium complexes or mono-and divalent copper complexes (454) (Scheme 3.192). Apparently, the catalyst initially forms a complex with imide (328), which reacts with nitronate (327) to give the key intermediate A. Evidently, diastereo- and enantioselectivity of the process are associated with preferable transformations of this intermediate. 

Li and co-workers examined the reaction between 1,2,3,4-tetrahydroisoquino-line and nitromethane, in which the nitromethane was used as a solvent, with various copper(I) and copper(II) salts. The desired aza-Henry product 6 was observed in all cases and CuBr was found to be the catalyst of choice. 

Kinetic investigations [32, 33] show dependencies, which are represented by Henry and Moiseev s equation (see Eq. (9.5)). Optimal technical catalysts have a deficit of the chloride ion concentration with respect to the Cu concentration. In a completely oxidized catalyst, the Cu + exists partly as copper oxychloride - its insoluble form has the composition Cu2(OH)3Cl. The chloride ion concentration controls the pH value of the catalyst and has, therefore, a great influence on the reaction rate. Figure 9.1 shows this correlation [6, 34]. 

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