Copper© triflate

Ally lie methylene groups can be converted to ester (—CHOCOR) derivatives in a similar manner using copper triflate. Cupric acetate has also been used as well... 

One important point to stress from these results is the possibihty of using copper chloride instead of copper triflate to prepare the complexes. It is well known that in organic solvents there is a dramatic counteranion effect on the activity and enantioselectivity of these catalysts. On the other hand, the rapid anion exchange produced in the ionic hquid resulted in better performance of the complexes, as the bis(triflyl)imide behaves in a similar way to the triflate counteranion. 

Aziridination of alkenes can be carried out using N-(p- to I ucncsu I I o n y I i m i n o) phenyliodinane and copper triflate or other copper salts.257 These reactions are mechanistically analogous to metal-catalyzed cyclopropanation. Rhodium acetate also acts as a catalyst.258 Other arenesulfonyliminoiodinanes can be used,259 as can chloroamine T260 and bromoamine T.261 The range of substituted alkenes that react includes acrylate esters.262... 

The hetero Diels-Alder reactions discussed thus far use 2-10 mol% of catalyst. Jorgensen s group44b found that the reaction could be carried out even at very low catalyst loading. The catalyst can conveniently be prepared in situ by mixing the chiral ligand 83 and copper triflate in the reaction system. Scheme 5-35 shows that product 112 can be obtained with good yield and high enan-... 

This class of donor is activated by soft Lewis acids, such as copper triflate at room temperature, and despite their hydrolytic instability, they appear inert to conditions of sulfoxide activation, TMSOTf or Tf20 (Scheme 4.53). Activation is achieved with stoichiometric promoter in the presence of the acceptor alcohol, and although the mechanism has not been investigated, presumably it proceeds via coordination followed by collapse to a stabilized oxacarbenium ion. The method is compatible with standard glycosidation solvents such as dichloromethane, acetonitrile and diethyl ether, and ester-directed couplings do not lead to orthoesters, perhaps as a result of the presence of the Lewis acid promoter [303,304]. 

Sibi and Chen demonstrated for the first time that relative and absolute stereocenters of both a and fJ> carbons can be controlled in the intermolecular addition trapping experiments (Scheme 55) [149]. Magnesium and copper Lewis acids performed better than zinc. The use of 30 mol % of chiral Lewis acid gave higher selectivities than the stoichiometric amounts for both magnesium and copper. Interestingly, copper triflate gave better selectivities with... 

The first catalytic, asymmetric aziridination of an alkene in good yield and high enantioselectivity was recently reported56. Thus styrene (63) was treated with [N-(p-toluenesulphonyl)imino]phenyliodinane (64) and an asymmetric copper catalyst to yield (/ )-Ar-(p-toluenesulphonyl)-2-phenylaziridine [(/ )-65] in 97% yield with an ee of 61%, the catalyst being the complex formed in situ in chloroform from the chiral bis[(5 ) 4-ferf-butyloxazoline] [(S,S)-66] and copper triflate (CuOTf)56, the reaction proceeding by way of a nitrene transfer57. 

Complete conversion of the substrate was observed with reaction times as short as 2.5 h when copper triflate was the Lewis acid, and the selectivity was usually greater than 98% towards the desired compound. Upon reuse of the same catalyst system with fresh substrate, it was reported that the conversion was 80% and 76% for the second and third reuse of the catalyst. 

The authors speculated that Pd(ii) was reduced by reaction with the IL, followed by formation of sigma complex between the olefin and copper triflate. This polarized complex then reacts with the Pd(0)-7r-complex with the substrate to form the final product as shown by the scheme below. Scheme 7. 

Heterocyclic amines have also been used in conjuction with copper catalysis, as shown by the copper triflate-catalyzed reaction of indole 140 with 5-bromopyrimidine 130, which gave the product 141 in quantitative yield... 

In 1997, Evans reported on the aldol reaction using the same enol ether 147 with a variety of glyoxylates and pyruvates using tin triflate and copper triflate. As shown in Table 9.26 (Fig. 9.47a), reaction of several pyruvates using bu-box ligand 3 complexed with copper(II) triflate afforded yields of up to 99% with selectivities up to 96% (ee) for adduct 150. " ... 

Finally, a recently reported copper catalyzed carbon-nitrogen bond forming process utilises reagents with polarity opposite to the common disconnection protocols. An electrophilic nitrogen, in most cases an (9-acyl hydroxylamine derivative, was successfully coupled with diarylzinc reagents in the presence of copper triflate or copper chloride. Di(2 -pyridyl)zinc and TV-benzoyloxy-morpholine were reacted at ambient temperature in the presence of 1% copper(I) triflate to give 2-morpholinopyridine in 71% yield (7.81.), Under these mild conditions the reaction was over in less than one hour.103... 

Takacs, J.M., Lawson, E.C., Reno, M.J., Youngman, M.A. and Quincy, D.A. (1997) Enantioselective Diels—Alder reactions Room temperature bis(oxazoline)-zinc, magnesium, and copper triflate catalysts. Tetrahedron Asymmetry, 8, 3073—3078. 

To introduce the chiral auxiliary, a labile anion, unlike the classical BFJ or PF which cannot be exchanged, is required. Preliminary studies showed the triflate to be appropriate. We introduced it during the formation step of the double helix. One equivalent of copper ) triflate was added to the bischelating diphenolic strand in a reductive medium. H NMR showed that the dinuclear copper dou-... 

Silver(I) triflate and copper triflate can be applied as catalysts A representative example is the preparation of alkynyl tosy lates by the catalytic decomposition of alkynyl lodomum salts in the presence of these salts [737] (equation 67)... 

The rhodium(II) catalysts and the chelated copper catalysts are considered to coordinate only to the carbenoid, while copper triflate and tetrafluoioborate coordinate to both the carbenoid and alkene and thus enhance cyclopropanation reactions through a template effect.14 Palladium-based catalysts, such as palladium(II) acetate and bis(benzonitrile)palladium(II) chloride,l6e are also believed to be able to coordinate with the alkene. Some chiral complexes based on cobalt have also been developed,21 but these have not been extensively used. 

The size of the silyl groups in compounds R3SiC(N2)COOMe influences their decomposition by copper triflate, dirhodium tetraacetate and dirhodium... 

Oxa-l -silabicyclo[ . 1,0 alkanes (n = 3 111 n = 4 113) were the only products isolated from the photochemical, thermal or transition-metal catalyzed decomposition of (alkenyloxysilyl)diazoacetates 110 and 112, respectively (equation 28)62. The results indicate that intramolecular cyclopropanation is possible via both a carbene and a carbenoid pathway. The efficiency of this transformation depends on the particular system and on the mode of decomposition, but the copper triflate catalyzed reaction is always more efficient than the photochemical route. For the thermally induced cyclopropanation 112 —> 113, a two-step noncarbene pathway at the high reaction temperature appears as an alternative, namely intramolecular cycloaddition of the diazo dipole to the olefinic bond followed by extrusion of N2 from the pyrazoline intermediate. A direct hint to this reaction mode is the formation of 3-methoxycarbonyl-4-methyl-l-oxa-2-sila-3-cyclopentenes instead of cyclopropanes 111 in the thermolysis of 110. 

For the transition-metal catalyzed decomposition of silyl-substituted diazoacetates 205 [silyl = SiMe3, SiEt3, SiMeiBu-i, SitPr-i SiPtnBiW, SiMe2SiMe3], copper triflate and dirhodium tetrakis(perfluorobutyrate) proved to be the best catalysts114. While these two catalysts induce the elimination of N2 at 20 °C even with bulky silyl substituents, dirhodium-tetraacetate even at 100 °C decomposes only the trimethylsilyl-and triethylsilyl-diazoacetates. When the decomposition reactions are carried out in... 

Cycloaddition of the carbene derived from 205 to bis(trimethylsilyl)acetylene yields the expected cyclopropene in low yield both photochemically (20%) and under catalysis by copper triflate at 80 °C (10-13%)119. The latter version of the reaction is accompanied by [3 + 2] cycloaddition of the diazo compound to the alkyne, and the photochemical route yields a by-product which obviously comes from carbenic C,H insertion at a SiMe3 group of the alkyne. 

Efforts to trap the carbonyl ylide intermediate by intramolecular [3 + 2] cycloaddition to a C=C bond were unsuccessful. Rather, the decomposition of allyl (trimethylsilyl)diazoacetate (218) (equation 69) in the presence of aldehydes gave 1,3-dioxolan-4-oncs 219 their formation has been explained by 1,5-cyclization of the carbonyl ylide intermediate followed by a Claisen rearrangement122. With acetone as carbonyl component, the reaction proceeds analogously. Clean formation of 219 occurred only with Rh2(OOCC3F7)4 as catalyst, while the copper triflate catalyzed version led to a mixture of 219, an oxirane and the product of intramolecular carbenoid... 

The synthesis of the 1,4-oxazepine 179 involved the formation of intermediate 178. The latter has been obtained by the three-component reaction of amine 175, aldehyde 176, and benzotriazole, leading to the intermediate 177, which underwent dehydrative cyclization to generate 178. Lewis acid-mediated cyclization with the loss of benzotriazole anion produced the interesting 1,4-oxazepine 179 (Scheme 29) <2001JOC5590>. A similar scandium or copper triflate-catalyzed reaction has been reported <1996SL871>. 

In a carbonyl-ene reaction of ethyl glyoxylate with a-methylstyrene catalysed by copper triflate-bisoxazoline complexes, ees of up to 100% have been achieved, but a dramatic switchover in stereochemistry is seen for an apparently minor change in bisoxazoline structure.185 A change in the metal geometry is implicated. 

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