Triflate anions, elimination

Triflate anions, elimination of 639 Triflinates, rearrangement of 669 Triflones 669... 

When the reaction between a-trifluoromethyl sulfone 286 and paraformaldehyde was carried out in the presence of potassium carbonate, the vinyl sulfone was obtained quantitatively upon elimination of triflate anion. Such a deacylative methylenation was observed in the reaction between 8-ketosulfones 287 and 288 and paraformaldehyde ... 

In an oxidative addition, Pd(0) complex 22 with BINAP as a ligand accepts alkenyl triflate It. The resulting Pd complex 23 is cationic, since the triflate anion is bound only loosely to the palladium and dissociates from the complex.1 Syn insertion of one of the two enantiotopic double bonds of the cyclopentadienc into the alkenyl-Pd bond of complex 23 leads firs to q -allyl-Pd complex 24. This is in rapid equilibrium with t 3-allyl-Pd complex 25. Neither 24 nor 25 contains a p-H atom in a yn relationship to palladium. Moreover, internal rotation is impossible in the con form a-tionaily fixed ring system. For this reason there is no possibility of a subsequent p-hydride elimination that would once again release the palladium catalyst. In a normal Heck reaction (see discussion) the catalytic cycle would be broken at this point. 

For example, styryl cations react with perchlorate to form covalent esters that are relatively stable at low temperatures [81], whereas the more basic triflate anion tends to abstract j3-protons from carbenium ions in a transfer reaction [56]. The basicity of the counteranion determines the contribution of /3-proton elimination relative to propagation, and therefore the limiting molecular weight in a polymerization. 

Even stronger adds than HC1 can be eliminated by proton transfer from jj2-H2 to the counteranion of highly electrophilic [L M]+. One of the strongest acids known, triflic acid, CF3S03H, can be eliminated from an H2 complex formed from H2 gas, as seal for reaction of a dicationic complex [Ru(OTf)(CNH)( L)J [OTf] (23, L = diphosphine) containing triflate anions and a protonated cyanide ligand, CNH.68 The crystal structure of 22, which is a weak Bipnsted base, shows a... 

We won t write a mechanism for the formation of the organothallium intermediate it forms via thallation of the enol form of acetophenone, and we urge you to write out the details. A triflate anion, which got kicked out in the first step, then displaces the thallium, which simultaneously undergoes reductive elimination to produce Tl OTf ... 

An example of cleavage ol the sulfur-oxygen bond in trifluoromethane-sulfonic ester has been reported Tnfluororaethyl triflate reacts with neutral or anionic nucleophiles with elimination of carbonyl difluoride and formation of trifluoromethanesulfonyl fluoride [57] (equation 32) The mechanism of this reaction involves elimination of fluoride ion, which is a chain carrier in the substitution of fluorine for the trifluoromethoxy group... 

The overall mechanism is closely related to that of the other cross-coupling methods. The aryl halide or triflate reacts with the Pd(0) catalyst by oxidative addition. The organoboron compound serves as the source of the second organic group by transmetala-tion. The disubstituted Pd(II) intermediate then undergoes reductive elimination. It appears that either the oxidative addition or the transmetalation can be rate-determining, depending on reaction conditions.134 With boronic acids as reactants, base catalysis is normally required and is believed to involve the formation of the more reactive boronate anion.135... 

From these observations, Woerpel and Cleary proposed a mechanism to account for allylic silane formation (Scheme 7.23).85 Silacyclopropane 94 is formed from cyclohexene silacyclopropane 58 through silylene transfer. Coordination of the Lewis basic benzyl ether to the electrophilic silicon atom86-88 generates pentacoordinate siliconate 95 and increases the nucleophilicity of the apical Si-C bond.89 Electrophilic attack by silylsilver triflate 96 forms silyl anion 97. Intramolecular deprotonation and elimination then affords the silylmethyl allylic silane. 

The progress of elimination (at 65 °C, in vacuum sealed CDC13 solutions) was monitored by lH and 29Si NMR spectroscopy, and was found to depend on the counterion among the halides the order of reactivity is I> Br> Cl [50% elimination after 85, 130, and 175 min, respectively, from 93c(Cl), 93c(Br), and 93c(I)], whereas the siliconium triflate 93c(OTf) did not react. It is thus evident that nucleophilic attack of the anion on one of the 7V-methyl groups is involved in the rate determining step of the elimination. 

When the anions of these acids are good leaving groups, elimination from their enol esters can be readily induced by comparatively weak bases. This is the case for p-bromobenzenesulphonates and triflates. Thus decarboxylative elimination from enol sulphonates 28 furnishes good yields of 2-alkynoic acids (equation 88), when R... 

C, and 457°C, respectively [127], Such high temperatures are only tolerated by most liquids for a short time. For example, after 10 h, even at temperatures as low as 200°C, [RMlm][PF ] and l-decyl-3-methyhmidazolium triflate show an appreciable mass loss [179], The ILs with low thermal stability are [EMIm][X], where X=[Tf N]-, [MjN]-, and Br [68], Phosphonium ILs with [Tf N]- or [NCCN) ]-anions decompose completely to volatile products in a single step. The degradation products indicate that Hofmann elimination process and/or dealkylation reactions occurred. Conversely, ILs based on nitrogen cations do not decompose completely... 

Asymmetric Wittig-Homer reactions Wittig-Horncr reactions have usually involved phosphine oxides, phosphonates, or phosphonamidcs. Highly enantioselcctivc ole-finations have now been achieved by use of this chiral phosphonamidatc 1. Thus the anion (t-BuLi) reacts with 4-/-butylcyclohexane to form 2 in >98% de. Elimination with trityl triflate/2,6-lutidine provides the alkylidene 3 with essentially complete stercospccificity. The reaction was shown to be applicable to a variety of 4-alkylcyclohexanones. 

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