Copper I Catalysts

The cationic nature of the copper(I) catalyst means that it is immobilized in the ionic liquid. This permits the PMMA product to be obtained, with negligible copper contamination, by a simple extraction procedure with toluene (in which the ionic liquid is not miscible) as the solvent. The ionic liquid/catalyst solution was subsequently reused. 

Jorgensen has recently reported similar enantioselective reactions between N-tosylimines 107 and trimethylsilyldiazomethane (TMSD) catalyzed by chiral Lewis acid complexes (Scheme 1.32) [57, 53]. The cis-aziridine could be obtained in 72% ee with use of a BINAP-copper(i) catalyst, but when a bisoxazoline-copper(i) complex was used the corresponding trans isomer was fonned in 69% ee but with very poor diastereoselectivity. 

These two compounds with S configuration on their oxazohne rings were tested as copper(I) catalysts for the cyclopropanation of styrene, the hgand 9 with S axial chirality being much more enantioselective than 10 with the R configuration. Thus, the catalytic system CuOTf-(S,S)-bis(oxazolyl)-binaphthyl (9, R = Bu) led to excellent enantioselectivities, particularly for the cyclopropanation of styrene with (-menthyldiazoacetate 95% ee for the trans-cyclopropane and 97% ee for the cis, with trans/cis = 68/32. 

The [3,3]-sigmatropic rearrangement ofpropargyl esters [234, 561] is usually an equilibrium reaction for example steric repulsion can help to deliver mainly the allene [562] and faster reaction kinetics are observed with silver(I) and copper(I) catalysts [562-571] (see cyclopropane 169 in Scheme 1.75) [572], and recently also rhodium(I) catalysts [573]. 

Gevorgyan and co-workers demonstrated that allenyl imines can be formed in situ by treating alkynylimines with a base (see Section 15.8, compound 185) [71, 72]. The same principle also works for the in situ formation of allenyl ketones from alkynyl ketones and their conversion to furans with a copper(I) catalyst [71, 72]. That Cu(I) would catalyze the isomerization of an allenyl ketone was known from work of Hashmi et al. [57, 58],... 

The organic base serves to remove the liberated protons and to assist solution of the copper(i) catalyst by the formation of a complex. Hydroxylamine hydrochloride helps to maintain an adequate concentration of copper(i) ions, which however is best kept rather low otherwise unwanted self-coupling of the bromoalkyne occurs. The reaction is illustrated in Expt 5.28 by the coupling of cu-bromophenylacetylene with 2-methylbut-3-yn-2-ol. 

Oxidative coupling of terminal acetylenes in the presence of copper(I) catalysts is the best method of preparing symmetrically substituted butadiyne derivatives,5 and has been applied to the coupling of trimethylsilyl-acetylene. Better yields are obtained using the Hay procedure in which the catalyst is the TMEDA complex of copper(I) chloride.7 The procedure submitted here is an improved version of Walton and Waugh s synthesis of BTMSBD by the Hay coupling of trimethylsilylacetylene.2 BTMSBD has also been prepared by... 

Numerous other examples of reactions of this type have been described and a particularly dramatic example of a product derived from oxygen atom transfer to a co-ordinated ligand is seen in the reaction of the benzimidazole ligand 9.16 with dioxygen in the presence of a copper(i) catalysts. The isolated product of the reaction is the copper(n) complex of the benzimidazole-3-carboxylic acid, 9.17. 

Alkenyliodonium salts can serve as highly reactive substrates in various transition metal-catalyzed reactions. In the presence of a copper(I) catalyst iodo-... 

For example, Jacobsen has studied the asymmetric aziridination of alkenes using (diimine)-copper(I)-catalysts 85. The results support the intermediacy of a discrete Cu(III)-nitrene intermediate and thus suggests mechanistic similarity (particularly regarding transition state geometry) to asymmetric cyclopropanation [95JA5889]. 

A more detailed view of the selectivities (Table 12.5) reveals a selective formation of the 2,4-disubstituted furan with the copper(I) catalysts (entries 1 and 2), a low... 

Enantioselective catalysis has also been used for the synthesis of optically active sulfimines [51]. By application of 5 mol % of the bisoxazoline-copper(I) catalyst 80, the sulfide 77 is oxidized catalytically to 78 which undergoes a [2,3]-sigmatropic rearrangement to give allyl amine 79 in 80% yield and with 58% ee (Eq. (20)). Other alkenes were found to give lower ee. 

Arylethynyl(trimethyl) silanes react with arylethynyl chlorides in the presence of copper(I) catalyst under neutral conditions without any base to give unsym-metrical diynes (Eq. 4) [10]. The reaction is thought to proceed via transmetala-tion of an alkynylsUane with a copper (I) complex. 

Copper(I) salts catalyze the allylic oxidation of alkenes in the presence of peresters, such as tert-BuOjCOPh, to afford the corresponding allylic benzoate esters. In the case of terminal alkenes, internal allylic esters are formed in preference over the terminal isomers. The mechanism is believed to involve addition of an allylic radical to copper(II) benzoate. " Rearrangement of the copper(III) intermediate then produces the product and regenerates the copper(I) catalyst. 

Gujadhur, R., Venkataraman, D. and Kintigh, J. T. (2001) Formation of aryl-nitrogen bonds using a soluble copper(I) catalyst. Tetrahedron Lett., 42, 4791 -793. 

Aube et al. developed methodology for single-electron transfer (SET) to oxaziridines under nonaqueous, neutral conditions <92JA5566>. Treatment of non-racemic 3-butenyloxaziridine (47) with the copper(I) catalysts [Cu(PPh3)Cl]4 gave pyrroline (48) in 95% ee and 66% yield (Equation... 

For the reaction of olefinic cosubstrates without activating groups copper(I) catalysts have to be used (Eq. 13). 

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