Copper triflate-catalyzed

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... 

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. 

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>. 

Copper The catalytic activity of copper(II) triflate for cyclizations of alkenols or intermolecular additions of alcohols and carboxylic acids to norbomene has been reported [62, 63]. In dioxane at 80°C, high conversions were achieved at prolonged reaction times, and those were superior to those obtained with Lewis acids such as Yb(OTf)3, though the latter also displayed catalytic activity [62]. In a control experiment with triflic acid (10 mol%) only little product (29%) resulted with low stereoselectivity. However, it is now clear that this control experiment was flawed, as too much triflic acid and overly long reaction times had been applied. The previously mentioned study by Carpentier and coworkers on copper triflate catalyzed hydroaUcoxylations has established that Cu(OTf)2 decomposes to CuOTf and triflic acid when heated in organic solvents [50]. Triflic acid is catalytically active in hydroaUcoxylation at levels down to 0.1 mol%, if a polymerization inhibitor is present to prevent consumption of the olefinic substrate. Indeed, Cu (OTf)2 is an excellent reagent for releasing small amounts of triflic acid in this case, because the coreleased CuOTf acts as polymerization inhibitor for the acrylic substrate (Scheme 12) [50]. Other metal triflates like Sc(OTf)3 or Yb(OTf)3 displayed catalytic activity at the 1 mol% level in the reaction of Scheme 12. Additional experiments were presented to support the conclusion that triflic acid is the actual catalyst in this and other Lewis acid catalyzed hydroalkoxylations [50]. 

Scheme 12 Copper triflate catalyzed intermolecular hydroalkoxylation of dicyclopentadiene...

Copper is mentioned among the water-sensible elements (Table 8.1). Accordingly copper triflate can be regarded as an efficient, economical, and safer alternative Lewis catalyst for the reactions carried out in water. An efficient microwave-assisted copper triflate-catalyzed reaction it was thus reported for the hydration of terminal aryl acetylenes affording substituted... 

Scheme 29 Copper triflate-catalyzed reactions of arylboroxines with N-nucleophiles...

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... 

Helmchen and co-worker investigated the use of phosphinooxazolines as ligands for copper(II) catalyzed Diels-Alder reactions (Scheme 19) (214). Optimal selectivities are found for a-naphthyl-substituted phosphinooxazoline (299). These catalysts require 2.5 h to induce complete conversion to cycloadduct, compared to 18 h using the triflate complex 269c under identical conditions. Helmchen invokes a square-planar metal geometry to explain the stereochemistry of the adducts, similar to the model proposed by Evans. He suggests that the bulky phosphine substituents are required to orient binding of the dienophile in such a way as to place the olefin directly below the terf-butyl substituent on the oxazoline. 

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... 

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... 

A copper(ll)-catalyzed cyclopropanation of the chromone derived benzylium triflates 1110 with the diazoester 1111 affords 2,3-cyclopropyl chroman-4-ones 1112 in good yield (Scheme 276) <2005TL4057>. 

Isolation of the air-sensitive silacyclopropene was avoided by development of a two-step, one-flask procedure, which transformed alkynes into the desired azasilacyclopentadienes (Scheme 7.29)." For terminal alkynes, silver phosphate was employed for di-terf-butylsilylene transfer and copper(I) triflate was used to promote nitrile insertion. These conditions successfully transformed phenylacetylene into azasilacyclopentadiene 106b. For internal alkynes, copper(I) triflate catalyzed both silylene transfer to 3-hexyne as well as nitrile insertion to produce enamine 106k. 

Following the publication of our method, similar procedures were reported by two other groups. One involves the use of bromamine-T as a nitrogen source instead of CT for the aziridination of olefins [14] the other is the copper(I) triflate-catalyzed aziridination and allylic amination with CT trihydrate [7d] (Schemes 8 and 9). 

Related allylic systems, such as enoates (12) bearing a phosphate leaving group are susceptible to copper-catalyzed Sn2 reactions. Employing copper triflate and a dialkylzinc, peptidic ligand (13) is especially effective at inducing asymmetry at the newly created stereogenic carbon a to the ester in (14) (equation 13). 

Table 11. Enantioselectivc Aziridination Catalyzed by Diimine-Copper Triflate Complexes 24...

Acylaziridines have been stereospecifically rearranged to give oxazolines, as illustrated by the copper(ll) triflate-catalyzed conversion of the chiral aziridine 259 into (-R)-oxytriphine 260. Mechanistically, this transformation is believed to proceed via initial coordination of the amide nitrogen with the azaphilic Lewis acid. This leads to the formation of an intermediate carbocation that exists as a tight ion pair in order to preserve the stereochemistry of the rearrangement (Scheme 69) <1998JOC4568>. 

Salomon has recendy investigated the coi er(I) triflate catalyzed photocycloadditions of allylic alcohols and allylic ethers in an effort to improve the selectivity in photocycloadditions of unactivated al-kenes (equations 103-105,108). ° One particularly interesting case is illustrated in equation (104), where Ae more sterically hindered product is produced as a result of the photocycloaddition of a rigidly held tridentate copper complex. McMurry has also utilized a copper(I) catalyzed [2 + 2] photocycloaddition in the synthesis of -panisene (equation 106)."° Interestingly, the noncatalyzed cycloaddition shown in equation (107), which might also produce a precursor for p-panisene, was unsuccessful. 

Diels-Alder reaction is one of the premiere reactions in synthetic organic chemistry. The traditional approach to the normal Diels-Alder reaction is to activate the di-enophile by means of a Lewis acid such that the transformation can be carried out under practicable conditions. A variety of Lewis acids catalyze this reaction selectively and among these copper(II) compounds have been very successful in enantioselective transformations. The use of bisoxazolines in combination with copper triflate or copper antimony hexafluoride has afforded high selectivity. Pioneering work in this area by Evans, Jprgensen, Kanemasa, and others has shed light on the different controlling features of the copper Lewis acids. 

An epoxide has been identified as an intermediate in the copper(I) triflate-catalyzed reaction outlined in equation (142). ... 

Various metal salts such as rare earth metal triflates and copper triflate can function as Lewis acids in aqueous media. They can effectively activate aldehydes and imines in the presence of water molecules, and the first successful examples of Lewis acid-catalyzed reactions in aqueous solution have been demonstrated. Water-soluble aldehydes such as foimaldehyde could be employed directly in these reactions. Moreover, the catalysts could be easily recovered after the reactions were completed and could be reused. There are many kinds of Lewis acid-promoted reactions in industrial chemistry, and treatment of large amounts of the acids left over after the reactions have induced some severe environmental problems. From the standpoints of their catalytic use and reusability, the Lewis acids described in this chapter are expected to be new types of catalysts providing some solutions for these problems. 

Arylcyclopropanes have also been prepared by metal-catalyzed carbene addition to 1,1-dimethylallene. When 4- and 3-nitrophenyldiazomethanes were decomposed with copper triflate in the presence of the allene, 2,2-dimethyl-3-methylene-l-(4-nitrophenyl)cyclopropane (7a) and 2,2-dimethyl-3-methylene-l-(3-nitrophenyl)cyclopropane (7b) were obtained in 62% and 38% yield, respectively. ... 

Ethyl diazoacetate (228 mg, 2.0 mmol) was added at a controlled rate over a 6-8 h period to a stirred mixture of the alkene (20.0 mmol) or diene (10.0 mmol) and the catalyst (0.01 -0,02 mmol) under and ordinarily at 25 C. For copper(I) triflate catalyzed reactions with enol ethers, the diazo ester dissolved in the enol ether w as added to copper(II) triflate in EtjO in order to minimize polymerization of the enol ether. Alkenes were generally purified by distillation prior to their use. The initial solubility of the transition metal compound was dependent on the alkene employed, and, with the exception of Rhg(CO)jg, bis(acetylacetonato)copper(II), and copper bronze, homogeneous solutions were obtained prior to or immediately after the initial addition of ethyl diazoacetate. 1 h after addition was complete, EtjO was added, the resulting solution was washed twice with sat. aq NaHC03 dried (MgSOJ. EtjO and excess alkene were distilled under reduced pressure. The desired cyclopropanes were obtained either by fractional bulb-to-bulb distillation or by preparative GC (Table 8). 

The success is attributed to the use of copper triflate as the copper source. The ligand catalyzes not only the reaction of cycloalkenone but also that of acyclic enones. The chiral thiazolidinone 23 (Scheme 14) was also developed as a chiral ligand to afford the product in 63% ee [57]. 

---