Acetalizations trifluoromethanesulfonic anhydride

Primary and secondary amides and thioamides react with alkyl chlorofoimates with loss of CO2 or COS, forming iminium chlorides (82 equation 52). In some cases this method is complementary to the Pinner imido ester hydrochloride synthesis. The iminium salt (83 Scheme 6) formed by action of ethyl chloroformate on DMF is labile and decomposes rapidly to ethyl chloride. If the reaction is performed in the presence of NaBp4, the iminium salt (85) is isolable. Aryl chlorofoimates react in the same fashion with DMF or DMA, but in these cases the aryloxymethyleneiminium compounds are fairly stable, so this reaction is an important method for the preparation of compounds of this type. - Succinic acid monoamides, phthalic acid monoamides and related compounds are cyclized to iminium salts (86 equation 53) by treatment with acetic anhydride and HC104. ° With the aid of trifluoromethanesulfonic anhydride lactams and amides can be converted to dication ether salts (87) and (88 Scheme 7).22i.222... 

Kim and co-workers carried out a closely related synthesis of a /<-(l -4)-mannote-traose 300, using their method for the in situ conversion of hemiacetals to glycosyl triflates by means of reaction with phthalic anhydride ( phthalan ) followed by trifluoromethanesulfonic anhydride. In this instance cleavage of the benzylidene acetal was effected with trifluoroacetic acid, and regioselective reprotection of the diol employed benzoyl chloride (Scheme 50).145... 

Acetals are one of a few groups of monomers for which the best general polymerization conditions can be given. Thus, if the aim is the preparation of high-molecular-weight polyacetals we would advise to use <0.1 mol % trifluoromethanesulfonic anhydride well below 0 °C in bulk. If the polymerization proceeds violently under these conditions and the time for mixing is insufficient to obtain uniform solution, both temperature and initiator concentration should be decreased. 

The benzo derivatives (41) and (42) of the disulfide dication (36) can also be prepared in the reaction of the corresponding 5 -oxides with cone. H2SO4. However, since the resulting bis(hydrogen-sulfate) salts are very hygroscopic, the structures are identified only on the basis of elemental analyses. The dication (36) is an intermediate in the Pummerer reaction of the S -oxide (37) with acetic anhydride, shown in Scheme 12, giving the a-acetoxylated product (43). However, when trifluoromethanesulfonic anhydride is used instead, the dication (36) can be isolated as a triflate... 

The Schiff base derivatives 73 of the 3-hetaryl-substituted 4-amino-3-thiol-l,2,4-triazoles, on treatment with acetic anhydride, undergo cyclization to give the corresponding 3-substituted-5-acetyl-5,6-dihydro-6-phenyl[l,2,4]triazolo[3,4-7][l,3,4]thiadiazoles 76 (Equation 16) <1990IJB135>. Similar treatment of 4-(A-bcnzoylamino)-4,5-dihydro-l-methyl-3-mcthylthio-1 //-[ 1,2,4 triazolc-5-thione 77 leads to the [l,2,4]triazolo[3,4-4][l,3,4]thiadiazolium trifluoromethanesulfonate 78 (Equation 17) <1986LA1540>. 

A non-aqueous method for the titration of procaine and other drugs using trifluoromethanesulfonic acid was reported by Zakhari and Kovar [88]. Solutions of procaine hydrochloride in anhydrous acetic acid, acetic anhydride, their mixture, or in acetone, was titrated with an acetic acid solution of 0.1 M trifluoromethanesulphonic acid or 0.1 M perchloric acid. Titration was effected in the presence or in the absence of mercurous acetate. The end point was detected visually (using crystal violet as indicator) or potentiometrically. 

Acetic acid, trifluoro-, anhydride with trifluoromethanesulfonic acid)... 

R)-(+)-2-Hydroxy-1,2,2-triphenylethyl acetate [(R)-HYTRA], To a mechanically stirred solution of (R)-(+)-1,1,2-triphenyl-1,2-ethanediol (35.0 g. 0.121 mol, Note 1) and acetic anhydride (17.1 mL, 0.181 mol, 1.5 eq, Note 2) in anhydrous acetonitrile (500 mL, Note 3) at room temperature under nitrogen is added a solution of scandium(lll) trifluoromethanesulfonate (1.23 g, 2.5 mmol, 2 mol%, Note 4) in anhydrous acetonitrile (125 mL) over approximately 35 min (Note 5). After about 8 min a white precipitate begins to appear, and the resulting mixture is stirred at room temperature under nitrogen for a total of 3 hr. The solid is filtered, washed with acetonitrile (2 x 25 mL), and dried under vacuum at 40°C overnight to afford (R)-(+)-2-hydroxy-1,2,2-triphenylethyl acetate (35.42 g, 0.107 mol, 88%) as a white solid (Note 6). 

Anodic oxidation of 4 -substituted 2-nitrobenzenesulfenanilide in CH3CN-ethyltributylammonium trifluoromethanesulfonate, containing 1% trifluoro-acetic acid and 1% trifluoroacetic anhydride, is reported to give 2,7-disubsti-tuted phenazines in 24-56% yield.113... 

Readion of anisole (1) with acetic anhydride was chosen as a model, and ytterbium trifluoromethanesulfonate (ytterbium triflate, Yb(OTf)3) was the first RE(OTf)3 representative used. Several reaction conditions were examined the results are summarized in Table 1. When acetic anhydride, acetonitrile, or nitromethane was used as a solvent (entries 4—10), the reaction mixture became homogeneous and the acylation reaction proceeded smoothly. Nitromethane gave the highest yield of4-methoxyaceto-phenone (2) (entries 7-10). On the other hand, in carbon disulfide, dichloroethane, or nitrobenzene (entries 1-3), the reaction mixture was heterogeneous and the yield of 2 was low. It was noted that the acylation proceeded quantitatively when a catalytic amount of Yb(OTf)3 was used (0.2equiv., entry 9). Even when 0.05 equiv. of the catalyst was employed, 2 was obtained in 79 % yield (entry 10). 

Other RE(OTf)3 were also examined as catalysts in the reaction of 1 with acetic anhydride (Table 2). Catalytic amounts of all the RE(OTf)3 listed effectively mediated the acylation of 1. Among these, scandium trifluoromethanesulfonate (scandium triflate, Sc(OTf)3)[6] or Yb(OTf)3 was superior to other RE(OTf)3 and afforded the acylation product 2 quantitatively. When, on the other hand, lanthanum trifluoromethanesulfonate (lanthanum triflate, La(OTf)3) was used, the yield of 2 was relatively low. The yields shown in Table 2 may reflect the catalytic activity of respective RE(OTf)3. 

Esters of very strong protonic acids (trifluoromethanesulfonic, fluoro-sulfonic, perchloric), however, are sufficiently strong alkylating agents to initiate the polymerization of even weakly nucleophilic monomers (cyclic acetals, ethers) [2-6], Also their anhydrides (e.g., triflic anhydride) are efficient initiators. This last compound is especially interesting, because in the polymerization of cyclic ethers it leads to macromolecules with two identical growing chain ends (difunctional initiator) [30] ... 

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