Mercuric triflate

Mercuric triflate has been shown to be a powerful catalyst for the cyclization of alkynyl /-butylcarbonates (36) and (37) giving rise to cyclic enol carbonates under mild conditions. Internal alkynyl carbonate (36) afforded the endo-dig cyclization (g) product (38) selectively, whereas terminal alkynyl carbonate (37) provided only the exo-dig product (39).48... 

The intermolecular Prins cyclization between ketones and homoallylic alcohols can be catalyzed by mercuric triflate <1999TL1153>. TMSNTf2 is an effective catalyst for the reaction between aldehydes and homoallylic alcohols <2002AGE161>. 

Recently, Nishizawa et al. reported a mercuric triflate [Hg(OTf)2]-catalyzed glycosylation using the alkynoate as the leaving group (O Scheme 61) [72]. 

Periana et al. have reported a mercury system that catalyzes the partial oxidation of methane to methanol.81 Hg(II) is typically considered to be a soft electrophile and is known to initiate electrophilic substitution of protons from aromatic substrates. The catalytic reaction employs mercuric triflate in sulfuric acid, and a key step in the catalytic cycle is Hg(II)-mediated methane C—H activation. For methane C—H activation by Hg(II), an oxidative addition reaction pathway via the formation of Hg(IV) is unlikely. Thus, an electrophilic substitution pathway has been proposed, although differentiation between proton transfer to an uncoordinated anion versus intramolecular proton transfer to a coordinated anion (i.e., o-bond metathesis) has not been established. Hg(II)-based methane C H activation was confirmed by the observation of H/D exchange between CH4 and D2S04 (Equation 11.9). 

The most common synthetic application of mercury-catalyzed addition to alkynes is the conversion of alkynes to ketones. This reaction is carried out under aqueous conditions, where the addition intermediate undergoes protonation to regenerate Hg ". Mercuric triflate has been found to be a useful reagent for this reaction. ... 

Synthesis of heterocycles using mercuric triflate as a catalyst 06Y744. 

This reaction has been adapted to primary acetylenic alcohol by treatment of the mixture of propargyl acetate and water with mercury(II) trifluoromethanesulfonate [mercuric triflate, Hg(Tf)2] to give vinyl ketones under very mild conditions. In addition, this reaction has been carried out at high temperatures without the addition of an acid catalyst. ... 

Propose a mechanism to explain how the mercuric triflate-catalyzed hydration of 126 produces 127. 

Several useful reviews have appeared this year. Synthesis-related reviews include the synthetic applications of selenium-stabilized carbenium ions/ the use of C-acylnitrilium ions to initiate cyclization in the synthesis of heterocycles/ and the involvement of carbocation intermediates in the cyclization of olefins with mercuric triflate. Solvolysis and rearrangement in unsaturated carbon cage compounds is reviewed/ backside r-bond assistance is suggested as being always involved." The Marcus equation is shown to be very useful in the determination of intrinsic barriers to the formation and reactions of carbocations. ... 

Methylene ethylene carbonate can be prepared in a good yield by mercury-catalyzed cyclization (54). Mercuric triflate (Hg(OTf)2), also called mercury(ll) trifluoromethanesulfonate, is a powerful catalyst for the cyclization of alkynyl terf-butylcarbonates giving rise to cyclic enol carbonates imder mild conditions. The S5mthesis is shovm in Figure 2.10. 

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mercuration/boration, undergo coupling with vinyl triflates (Entry 10). 

Glycoside synthesis from 2-pyridylthio glycosides is also possible with 0-benzyl-protected donors in the presence of methyl iodide [20], silver triflate [21 ], or mercuric salts [10,13,22], The versatility of this leaving group has also been demonstrated in the synthesis of C-glycosides [23 J. 

Vinylidenes have been transferred from a variety of precursors to olefins to produce methylenecyclopropanes . Because of ready intramolecular hydrogen shifts to give terminal acetylenes, the addition of vinylidene to olefins is rather limited to 2,2-disubstituted species. The methodologies so far developed include (1) gem-dibromides, 7, with MeLi, (2) vinyl halides " or vinyl triflates, 8 " with r-BuOK, (3) the fluoride ion promoted decomposition of vinylsilanes, 92 2,243 4 thermolysis of mercuric derivatives, 10, at 250 (5) decomposition of vinylazo compounds, 11, at 25 (6) the alkaline... 

Oxazolidines are obtained in good to excellent yields by the palladium(II)-catalyzed cyclization of A-Boc protected iV-allyl-A -hydroxymethylamines (191) <94CC357>. The palladium species is regenerated by molecular oxygen in DMSO (Scheme 94). Allyl carbamoylmethyl ethers cyclize to oxazolidines by reaction with mercuric acetate <89H(28)663>. Silver triflate catalyzes the cyclization of (9-propargyl isoureas to 4-alkylidene-oxazolidines with high diastereoselectivity <88CC1175>. 

Intramolecnlar alkenylation at a furan a- or P-position by an alkyne occurs, with the formation of bicycUc derivatives, when promoted by mercury(II) acetate (or Hg(OAc)(OTf), generated in situ from mercuric acetate and scandinm triflate). In the case of closure onto a p-position, a spirocyclic intermediate from preferred attack at the a-position, may be involved, as shown. 

The Suzuki method for cross-coupling involves use of an arylboronic acid as the nucleophilic component. These conditions have been successfully applied to indoles. Indole-3-boronic acids, which can be prepared via electrophilic mercuration, can be coupled with vinyl triflates (Scheme 130) <93TL2235>. 

Dynamics in molecules containing metals can rely heavily on the spectral changes of the metallic nucleus. Intermolecular exchange of ligands on mercury, for example, can be followed by examination of the Hg spectra. Peringer and Winkler (13) observed Hg line broadening of phenylmercuric triflate in the presence of mercuric ion and demonstrated that the dynamic effect arose from the process of eq. 3. A molecule of the type 5 poses... 

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