Trifluoromethanesulphonates, esters

A very efficient method of introducing iodide (and presumably other nucleophiles) into carbohydrates involves the use of trifluoromethanesulphonate esters and their displacement with tetrabutylammonium iodide in refluxing benzene. Several monodeoxymonoiodo compounds were made in this way including compounds (17) and (18) which are difficult to obtain by more usual methods. ... 

Ethyl trifluoromethanesulphonate [425-75-2] M 178.1, b 115 /atm, 118-120 /atm, d 1.378, Up 1.336. The ester reacts slowly with H2O and aqueous alkali. If its IR has no OH bands (-3000 cm ) then purify by redistillation. If OH bands are present then dilute with dry Et2O and shake (carefully) with aqueous NaHCO3 until effervescence ceases, then wash with H2O and dry (MgSOa), filter, evaporate and distil the residue under slight vacuum then at atmospheric pressure in a N2 atmosphere. IT IS A POWERFUL ALKYLATING AGENT, AND THE FUMES ARE VERY TOXIC - CARRY ALL OPERATIONS IN AN EFFICIENT FUMECUPBOARD. [Gramstad and Hazeldine JCS 173 7956 Howells and McCown Chem Reviews 77 697977]. 

Solutions of carboxylic acids or anhydrides in strong mineral acids also give rise to the protonation of the weaker component, but often the reaction goes further and leads to the formation of acylium ions. Thus, in the case of acetic acid dissolved in such strong acids as sulphuric, perchloric and trifluoromethanesulphonic acids, dehydration of the protonated species (ACOH2) gives the corresponding acetyl ester and/or its ionised form. The same endproduct is obtained if acetic anhydride is used instead of its acid ... 

In 1985, lhara et al. [51] described a short synthesis to ( )-tylophorine [(+)- ] via an effective, mild annelation by reacting an a,P-unsaturated enamide ester with trialkysilyl trifluoromethanesulphonate (TBSOTf) and triethylamine. The enamide esters (22), prepared by Wittig reaction of 21, were treated with an equimolar amount of TBSOTf and EtsN in CH2CI2 at ambient temperature to afford 23 in 68% yield. Oxidation of... 

Esterification of sulphonic acids with alcohols usually produces an equilibrium mixture. For example, reaction of trifluoromethanesulphonic acid with ethanol gives an equilibrium mixture of diethyl ether, the ester and the reactants383,384. Such an equilibrium may be driven to give the desired sulphonate ester by azeotropic removal of water385. 

A different approach to a-methylenebutyrolactones is a further development of the chemistry of 2-silyloxycyclopropane carboxylates (393), which, when treated with the trifluoromethanesulphonate analogue of Eschenmoser s salt and a Lewis acid (TMSOTf), are converted into 8-amino-esters (394) and thence lactones (395) following borohydride reduction and elimination.33 Overall yields are reasonable for this multi-step approach. A carbanion based approach to monosubstituted lactones. (390) begins by metallation and regio-selective condensation of ketene dithioacetal (396) with an aldehyde. 

Aminations which afford 6-aminocarboxylates are of interest in relation to monobactam antibiotics. A secondary aminomethyl group can be introduced at the -position of carboxylic esters by reaction of hexahydro-1,3,5-triazines with ketene silyl acetals in the presence of a catalytic quantity of trifluoromethanesulphonic acid (Scheme 25). The triazine (10) is considered to be converted into an N-silylated methyleneiminium salt which undergoes addition of the ketene silylacetal (11). 

Two further reactions might be included here, since they involve modification at both carbon and sulphur. In the first reaction, dehydration of the sulphoxides 388 (R = Me or aryl R = H, Me, ethenyl or Ph) to the diethyl [(l-alkylthio)alk-l-enyl]phosphonates 389 is said to result following the action of trimethylsilyl trifluoromethanesulphonate The second reaction constitutes a new and improved synthesis of an ester of (mercap-tomethyl)phosphonic acid, and consists in the treatment of methyl (diisopropylphosphi-noyl)dithioformate with NaBH4. ... 

Latterly, attention has been turned to the alkylation of the hydrogenphosphonates themselves under essentially neutral conditions, thus obviating the several possible side reactions. The formation (in 38% yield) of triethyl phosphonoacetate from diethyl hydro-genphosphonate and ethyl diazoacetate has been known for some time, and the synthetically useful methyl (di-tcrt-butoxyphosphinoyl)acetate (in 40% yield) has been similarly and more recently obtained Steps have been to tiy to improve yields under photoinitiation in the presence of copper salts or complexes ", or through catalysis by trifluoromethanesulphonic acid Such procedures allow the ready synthesis of the esters 411 (R = alkyl or RO). 

Dibromomalonates have been recommended as good sources of bromonium ions in the preparation of a-bromoesters from ester enolates. Trimethylsilyl trifluoromethanesulphonate is useful for the preparation of a-trimethylsilyl esters directly from esters.Little of the corresponding silyl enolate is formdd. 

Polymerizations of THF initiated by strong protonic acids can be propagated by both ions and esters. Temperature, monomer conversion, and the nature of the solvent influence the equilibrium between the two types of active centres. The anhydrides of certain acids e.g. trifluoromethanesulphonic acid) may be used to initiate bifunctional living polymers of THF. Under certain conditions... 

Two other trialkylsilyl trifluoromethanesulphonates, the TBDMS and tri-isopropylsilyl (TIPS) compounds, have been prepared and used in silylation reactions catalysed by 2,6-lutidine " TBDMS triflate allows formation of TBDMS ethers from tertiary and unreactive secondary alcohols, and TIPS triflate reacts effectively with primary and secondary alcohols. Use of the perfluorinated resin sulphonic acid trimethylsilyl ester Nafion-TMS , an immobilized TMS triflate, as a silylating agent for alcohols cf. 5,167) is discussed in a publication on applications of TMS triflate in synthesis. ... 

Not surprisingly, trifluoromethanesulphonic acid can be used effectively as catalyst for the Fischer glycosidation of free sugars, and phosphorus oxychloride catalyses the reaction between sugar peracetates and alcohols. For aryl, alkyl and aralkyl D-glucoside esters /9-anomers (the kinetic products) are favoured if the reactions are carried out in benzene solution, whereas the more stable o-products predominate if no solvent is used. °... 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

General Synthesis and Reactions of Esters.— Esters and lactones are formed from ketones under aprotic conditions, using bis(trimethylsilyl) peroxide and a catalytic amount of trimethylsilyl trifluoromethanesulphonate yields for ten examples are between 24 and 76%. The reaction occurs specifically at the carbonyl group and carbon-carbon double-bonds are not affected. " Aldehydes are converted into methyl esters with a solution of sodium hypochlorite and methanol in acetic add yields of between 22 and 90% are obtained for seven examples. A similar reaction involves the treatment of an aldehyde with t-butyl hypochlorite followed by an alcohol yields are between 39 and 98% for six examples (Scheme 34). ... 

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