CuOTf cycloaddition

The presence of an oxygen atom in the chain linking the two alkene moieties does not appear to affect the efficiency of the cyclizations encountered. Thus, the (2 + 2)-intramolecular cycloaddition of the divinyl ether 101a in ether solution with CuOTf... 

Copper(I) catalysis is very well established to promote intramolecular [2+2] photocycloaddition reactions of l,n-dienes (review [351]). The methodology recently enjoyed a number of applications [352-354], It is assumed that CuOTf, which is commonly applied as the catalyst, coordinates the diene and in this way mediates a preorganization. The Ghosh group recently reported a number of CuOTf-catalyzed photochemical [2+2] cycloaddition reactions, in which an organocopper radical complex was proposed as a cyclization intermediate (which should, however, have a formal Cu(II) oxidation state) (selected references [355-357]). A radical complex must, however, not be invoked, since the process may either proceed by a [2+2] photocycloaddition in the coordination sphere of copper without changing the oxidation state or according to a cycloisomerization/reductive elimination process. 

Thus, metal-catalyzed decomposition of 10a in the presence of an equimolar amoimt of benzaldehyde generates the carbonyl ylide 21 which can be trapped with a suitable electron-poor dipolarophile to give tetrahydrofiirans 23, 24, and dihydrofuran 25, respectively. These heterocycles were obtained as sole products in 41-62 % yield when Rh2(pfb)4 or [Ru2(CO)4(OAc)2] were used as catalysts, whereas catalysis by CuOTf afforded mainly the oxirane 22 (38 %) besides some cycloaddition product (23 11.5% 24 16%). 

An example of complexation of Ji bonds is illustrated in the isomerization reaction shown in Sch. 39. Use of copper chloride enables the efficient conversion of the cis olefin 168 to the trans olefin 169 [77]. (CuOTf)2(C6Hg) can be readily prepared (or purchased) and has been used for [2 + 2] photocycloaddition. An example of norbor-nene dimerization is shown below in which the Cu(I) forms a n complex with two molecules of the olefin and enables a facile cycloaddition.[51]... 

More modern studies have made use of copper(I) triflate (CuOTf) as the reagent. This compound is well known to form complexes with dienes and it provides a template on which cycloadditions can be effected. Several examples of this type of cyclization have been reported and cycloadditions based on this approach provide a useful route to cyclobutane derivatives. Thus, a new stereochemical synthesis of grandisol has been developed using the copper(I)-catalysed cycloaddition of the dienol 95 to afford the isomeric bicyclo-heptenols 96 exo endo ratio in this cyclization is solvent-dependent. The racemic... 

Addition and cycloaddition. Two slightly different protocols are available for achieving addition of 1-alkynes to trifluoromethyl ketones use either CuOTf and t-BuOK with Xantphos in THF at 60°, or Cu(OTf)2 and two equivalents of t-BuOK and 1,10-phenanthro-line in toluene at 100°. Cyanoformate esters can contribute the CN group as an addend to react with organoazides in a [3+2]cycloaddition catalyzed by CuOTf. ... 

Cycloadditions. A chiral 2,2 -bipyridine (69) in which each nucleus is fused to a ferrocene has found use in a CuOTf-catalyzed asymmetric cyclopropanation. "" ... 

Cycloaddition.—Herndon has reviewed substituent effects in photocycloaddi-tions. Copper(i) triflate is found to be an effective catalyst for the photodimerization of norbornene to the usual [2 + 2] dimer. Photoexcitation of a 2 1 alkene-CuOTf complex is suggested. The photodimerization of other simple alkenes is also... 

The involvement of a transient photogenerated irans-cyclohe-xene-CuOTf intermediate was also adduced to explain CuOTf catalysis of photoinduced 2jr + 4jr cycloaddition between cis-cyclohexene and 1,3-butadiene (eq 17). In contrast to thermal Diels-Alder reactions, this reaction generates ira/js-A -octalin rather than the cis cycloadduct expected for a 2its +Aits cycloaddition. A mechanism was proposed that involves the 2ns +4jrs cycloaddition of a fraas-cyclohexene with 1,3-butadiene in the coordination sphere of Cu (eq 18). ... 

That CuOTf-catalyzed 2n + 2n photocycloadditions are not restricted to cyclic alkenes was first demonstrated in mixed cycloadditions involving allyl alcohol. To suppress homodimerization of e/jcto-dicyclopentadiene (i.e. eq 11) the diene to Cu ratio is maintained at < 1 1 and allyl alcohol is used as solvent. Under these conditions, a high yield of mixed cycloadduct is generated (eq 19). ... 

CuOTf-promoted elimination of thiophenol was exploited in two syntheses of 1-phenylthio-1,3-butadiene, one a C-C connective route from allyl bromide and bis(phenylthio)-methyllithium, and another from crotonaldehyde (eq 49). A topologically analogous C-C connective strategy provides 2-methoxy-1-phenylthio-1,3-butadiene from acrolein (eq 50). That the phenylthio rather than the methoxy substituent in 2-methoxy-1-phenylthio-1,3-butadiene controls the orientation of its Diels-Alder cycloadditions is noteworthy (eq 50). 

Use of an imine in conjunction with diazoacetates allows the formation of an azomethine yUde intermediate that can undergo a 1,3-dipolar cycloaddition with a suitable dipolarophile. Based on this strategy, CuOTf efficiently catalyzed a three-coir onent assembly reaction for the synthesis of 2,5-frans-pyrrolidines... 

Intermolecular cycloaddition reactions catalyzed by Cu(I) were studied by Salomon and Kochi, by Mackor and by others. The use of better soluble CuOTf instead of Cu-halides allowed reactions to be run more effectively and cleaner. Reactions studied are the 2 -t- 2 cycloaddition of norbomene giving the exo-trans-exo isomer exclusively (97 %), the analogous reaction with e d(9-dicyclopentadiene as substrate, the codimerization of norbomene with cyclooctene, the dimerization of cyclopentene, cyclohexene, cyclo-heptene and mixtures thereof. 

Cu(I) complexes have also played a role in the much studied nor-bomadiene (NBD)-quadricyclene (QC) interconversion [21], Irradiation into the olefin-Cu CT band decreases the double bond order and facilitates internal 2 + 2 cycloaddition. The Cu(I) species employed was Cu(CO)pzb (pzb = trispyrazolylborate). Addition of NBD causes a spectral change with appearance of a new band at 293 nm indicating the formation of an NBD complex. Note that in this case, different from the CuX or CuOTf catalysts, three coordination sites at the metal are firmly occupied by the chelating pzb... 

CuOTf-catalyzed synthesis of polysubstituted pyrroles from a-diazoketones, nitroalkenes, and amines was reported by Lu, Wang, and coworkers. The corresponding polysubstituted pyrroles could be obtained in moderate yields using air as the oxidant. This cascade process of the polysubstituted pyrrole formation involves an NH insertion of carbene, a copper-catalyzed oxidative dehydrogenation of amine, and a [3+2] cycloaddition of azomethine ylide [21] (Scheme 8.9). 

The competition between Michael addition and 1,3-dipolar cycloaddition has been investigated for the reaction of alkylidene bisphosphates and alkylidene malonates PhCH=CX2 [X = P(0)(0R)2 or CO2R] with azomethine ylides (generated from PhCH=NCH2C02Me) catalysed by the CuOTf-BiphamPhos complex. ... 

Irradiation of cyclohexene in the presence of CuOTf produces the dimers 14 (49%) and 15 (8%), along with the cyclohexylcyclohexene 16 (24%) (Scheme 5)T The stereochemical outcome in Cu(I)-catalyzed dimerization of cyclohexene may be the result of cis-tram isomerization on irradiation of the initially formed Cu(I)-cyclohexene complex to the trans-cyclohexene-CuOTf complex 13, followed by a concerted ground state 2 + 2 cycloaddition of the highly strained tram-cyclohexene to another cyclohexene. Cycloheptene, on the other hand, produces the aU tra s-fused trimer 17 (Scheme 6) as the sole product. A 1 3 CuOTf-trans-cycloheptene complex has been proposed to be the precursor of this product. No dimerization reaction has been observed for cyclooctene and acychc olefins.However, mixed photocycloaddition occurs with cyclooctene if the other olefin is sufficiently reactive. Thus, cyclooctene adds to norbornene to produce the cyclobutane derivative 18 in 40% yield. GDdimerization was also observed when a mixture of cyclohexene and cycloheptene was irradiated in the presence of CuOTf to yield the adduct 19 (Scheme 6). ... 

The involvement of a transient photogenerated trans-cyclohexene-CuOTf intermediate was also adduced to explain CuOTf catalysis of photoinduced 2-ir+4-ir cycloaddition between cis-cyclohexeneand 1,3-butadiene (eq 17). In contrast to thermal... 

On the other hand, metalated acetylides can promote the cycloaddition reaction and form a stable 5-metalated triazole ready to be functionalized at this position. Thus, stable, easily accessible, nontoxic, and diversely substituted l-bismuth(III) acetylides undergo an efficient cycloaddition with organic azides in the presence of 5 mol% CuOTf in THF, under mild conditions to form stable 5-bismuth(III) triazolides in yields from 60% to 91%. In this study, it is hypothesized that there is a weak and reversible % interaction of the copper(I) catalyst with bismuth(III) acetylide [34, 35]. 

---