Trifluoroacetic anhydride sulfoxide

Treated with trifluoroacetic anhydride, sulfoxides 218 undergo conversion to triazapentalenes 219 with high yields. The process must involve acylation of the sulfoxide oxygen atom and generation of a carbocation that attacks the N-2 atom of benzotriazole. Hydrogenation over Raney nickel cleaves the C-S and one of the N-N bonds to generate >rtfe -substituted anilines 220 (Scheme 27) <2002EJ0493>. 

Dimethyl sulfoxide reacts with trifluoroacetic anhydride at low tempera ture to give a complex that is an efficient reagent for the oxidation of alcohols to carbonyl compounds [40 41] This reagent can be used to oxidize primary and secondary aliphatic alcohols, cycloalkyl alcohols, and allylic, homoallylic, ben-zylic, acetylenic, and steroidal alcohols (equation 19)... 

The synthesis of 4,5-diaryl-6-phenylsulfanyl-2,3-benzo-l,3a,6a-triazapentalenes 239 through Pummerer-type reactions of (benzotriazol-l-yl)allylic sulfoxides 238 with trifluoroacetic anhydride in THF has been reported (Equation 35) <2002EJ0493>. Similarly, unstable solid imines 240 treated without purification with trifluoroacetic anhydride (TFAA) provide 241 (Equation 36) <2003TL7507>. 

The differing nucleophilicity of acetate and trifluoroacetate anion determined the manner in which naphtho[l,8-/yt]-l,5-dithiocinc sulfoxide 127 rearranged on treatment with acetic and trifluoroacetic anhydrides. In both cases, the reaction proceeded through formation of a disulfonium dication 128, but the final products were different. When acetic anhydride was used, the reaction afforded the corresponding a-acetylsulfide 130, a normal product of the Pummerer rearrangement, while trifluoroacetic anhydride caused isomerization with formation of dithioacetal 132 (see Scheme 16) <1995HAC559>. 

Reaction of -dimethylthiobenzene sulfoxide 56 with trifluoroacetic anhydride results in a mixture of sulfide 65 and the corresponding mono- and disubstituted products of the Pummerer rearrangement 63, 64 via intermediate disulfonium dication 62 (Scheme 23).88... 

The reduction of (2,3)-q - and (2,3)-jS-methylenepenam j6-sulfoxides to the corresponding sulfides using potassium iodide and trifluoroacetic anhydride (TFAA) is found to be much faster than for bicyclic jS-lactam jS-sulfoxides.- In the proposed mechanism, initial attack of the sulfoxide oxygen on TFAA is followed by rate-limiting, nucleophilic displacement of trifluoroacetate by iodide ion nucleophilic attack of iodide on the iodine atom then yields the sulfide and iodine. The rate enhancement is accounted for by the stabilization of the transition state in the rate-limiting step by interaction of the p-like orbital of sulfur and the cyclopropane a orbital. 

Chemical deoxygenation of sulfoxides to sulfides was carried out by refluxing in aqueous-alcoholic solutions with stannous chloride (yields 62-93%) [186 Procedure 36, p. 214), with titanium trichloride (yields 68-91%) [203], by treatment at room temperature with molybdenum trichloride (prepared by reduction of molybdenyl chloride M0OCI3 with zinc dust in tetrahydrofuran) (yields 78-91%) [216], by heating with vanadium dichloride in aqueous tetrahydrofuran at 100° (yields 74-88%) [216], and by refluxing in aqueous methanol with chromium dichloride (yield 24%) [190], A very impressive method is the conversion of dialkyl and diaryl sulfoxides to sulfides by treatment in acetone solutions for a few minutes with 2.4 equivalents of sodium iodide and 1.2-2.6 equivalents of trifluoroacetic anhydride (isolated yields 90-98%) [655]. 

Benzothiazine ylides can be prepared by reaction of a sulfoxide with trifluoroacetic anhydride followed by an intramolecular nucleophilic attack of enamine and elimination of OAc from the sulfur (Equation 56) <1982J(P1)831, 1991J(P1)2249>. An interesting variation is the replacement of the enamine with an aniline (Equation 57) <1997JCM416>. 

Alternatively, when 21 was treated with benzaldehyde diethyl acetal-hydrochloric acid, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (76) was formed in >90% yield. Diacetal 76 was efficiently oxidized to 77 (>90% yield) with dimethyl sulfoxide-trifluoroacetic anhydride, or by way of the nitrate of 76 and triethylamine. Hydrolysis of 77 then afforded ethyl L-xy(o-2-hexulosonate in 86% yield.383... 

Brief treatment of the sulfoxide 1 with trifluoroacetic anhydride in refluxing toluene gives the dihydronaphthalene 2 in 55% yield as a single regioisomer... 

The latter, on reaction with methylamine yielded via the P-epoxide 373, the trans-a aminoalcohol 374, which was N-acylated to the amide 375. Acid-catalysed dehydration of the tertiary alcohol 375, led to the olefin 375, from which the key radical precursor, the chlorothioether377 was secured in quantitative yield by reaction with N-chlorosuccinimide. In keeping with the earlier results recorded for structurally related compounds, 377 on heating in the presence of ruthenium dichloride and triphenylphosphine also underwent a 5-exo radical addition to generate the cyclohexyl radical 378 which recaptured the chlorine atom to furnish the a-chloro-c/5-hydroindolone 379. Oxidation of thioether 379 gave the corresponding sulfoxide 380, which on successive treatment with trifluoroacetic anhydride and aqueous bicarbonate led to the chloro-a-ketoamide 381. The olefin 382 resulting from base induced dehydrochlorination of 381, was reduced to the hydroxy-amine 383, which was obtained as the sole diastereoisomer... 

Interaction of the sulfoxide with some acid anhydrides or halides may be explosive. The highly exothermic reaction with trifluoroacetic anhydride was adequately controlled in dichloromethane solution at below —40°C. 

Trifluoroacetic anhydride [407-25-0] p O O p F F Dimethyl sulfoxide See Dimethyl sulfoxide Trifluoroacetic anhydride Nitric acid, l,3,5-Triacetylhexahydro-l,3,5-triazine See Nitric acid 1,3,5-Triacetylhexahydrotriazine Nitric acid, 1,3,5-Triazine See Nitric acid 1,3,5-Triazine, etc. See other ACID ANHYDRIDES c4f6o3... 

Lithium Aluminum Hydride. Reacts violently with trifluoroacetic acid.2 Dimethyl Sulfoxide. Reacts explosively with trifluoroacetic anhydride.3... 

The reduction of penam sulfoxides to their corresponding sulfides can be done by treatment with either phosphorus pentasulfide/pyridine in dichloromethane <1993H(36)1529> or trifluoroacetic anhydride/KI in acetone <1998TL8537>. 

Trifluoroacetic anhydride effects the cyclization of 3-phenylpropyl methyl sulfoxide to the thiochromanium salt 490 in high yield. Demethylation to thiochroman is readily achieved by treatment with diethylamine (Scheme 178) <1996SLJL75>. 

Ube Industries LtdinYamaguchi, Japan, and Kyoto University investigated the Swern oxidation for pharmaceutical intermediates [57,58]. In this reaction, alcohols are oxidized to carbonyl compounds using dimethyl sulfoxide. The reaction variant using dimethyl sulfoxide activated by trifluoroacetic anhydride (shown below) has found industrial application, but is limited to low-temperature operation (—50 °C or below) to avoid decomposition of an intermediate. 

In a microscale tubular reactor, Swern oxidations were performed between —20 and 20 °C. Mixing was performed stagewise with a series of rapid mixing functions (see Figure 5.22) [57,58]. First, dimethyl sulfoxide and trifluoroacetic anhydride were contacted in an interdigital micromixer followed by a stainless steel tube reactor Rl. After addition of the alcohol and reaction in reactor R2, the mixture was then contacted with a triethylamine solution and passed through two more reactors (R3 and R4) to complete the reaction. 

Padwa and Kuethe have also used vinylogous Pummerer reactions of amido sulfoxides in the preparation of nitrogen-containing heterocycles. Vinyl amido sulfoxide (224) underwent an additive Pummerer reaction, on treatment with trifluoroacetic anhydride, to yield product 226 (Scheme 57).123 The a-thiocarbo-cation 225 generated from the Pummerer reaction of N-methyl-N-phenyl-2-[2-(toluene-4-sulfinyl)phenyl]acetamide (224) underwent a Friedel-Crafts reaction at the y-carbon with the tethered aromatic ring. Reductive removal of the... 

The reaction of phenyl vinyl sulfoxide 234 with isobutene, in the presence of trifluoroacetic anhydride, yielded the to-alkylated product 238 (Scheme 59).128 It was suggested that this reaction proceeded by a different mechanism than the usual additive Pummerer mechanism. The alkene reacts with the electrophilic sulfur atom of intermediate 235, giving, after loss of a trifluoroacetate ion and a proton, the sulfonium ion 236. Thio-Claisen rearrangement of the ion then gives the thonium ion 237 which reacts with a further molecule of isobutene to give the product 238. 

Unsaturated ketones are known to react with dichloromethyl phenyl sulfoxide to give adducts which produced fully substituted furans in high yields after treatment with trifluoroacetic anhydride and Nal, as illustrated in the following scheme. Trisubstituted... 

Participation by aromatic rings is also possible and there are now several examples of electro M]ic aromatic substitution involving Pummerer intermediates. Equation (20), the alkylation of benzene with dimethyl sulfoxide in trifluoroacetic anhydride, illustrates the process in its inq>lest foim. As widi al-kenes, reaction with aromatics has been more widely exploit in intramolecular versions for the construction of carbocycles and heterocycles. In many cases the sulfoxide precursor is of the keto variety, thus ensuring regiospecificity in the point of cyclization. Equation (21) (formation of a six-monber carbocycle), equation (22) (formation of a six-membered sulfur heterocycle), equation (23) (formation of a six-membered nitrogen heterocycle) and equation (24) (formation of a seven-membered nitrogen, sulfur heterocycle) provide illustrations of the versatility of diis form of intramolecular aromatic alkylation. 

Trifluoroacetic anhydride upon mixing with dimethyl sulfoxide can undergo a violent reaction at or just below room temperature. However, it is possible to moderate this behavior by working at temperatures below -60 C in an inert solvent such as dichloromethane, when dimethyl sulfoxide and tiifluo-roacetic anhydride react exothermically and instantly to foim a white precipitate, which is most probably the species (12). 

Thionyl chloride appears to be siqrerior to trifluoroacetic anhydride as an activator of dimethyl sulfoxide during the oxidation of alcohols in terms of yields of carbonyl compounds, although it has not been as widely used. The active species in this process, leading to an alkoxysulfonium species, is probably the ion pair (26). 

As with trifluoroacetic anhydride, activation of dimethyl sulfoxide with thionyl chloride must be carried out at low temperatures as the reaction is highly exothenmic. Besides the higher yields, a further advantage of thionyl chloride to activate dimethyl sulfoxide over anhydrides is the lack of Pummerer rearrangement products or of esters formed as by-products (as long as Ae reactions are carried out below -60 C). This is amply demonstrated by the oxidation of (-)-bomeol which proceeds in an excellent 99% yield (equation 12). ... 

Although many oxidizing reagents remove the chromium tricarbonyl group, benzylic alcohols can be oxidized to benzaldehydes using dimethyl sulfoxide with acetic anhydride, trifluoroacetic anhydride, or sulfurtrioxide with minimal decomplexation. Asymmetric oxidation of aUcylthio-substituted complexes can be achieved using titanium tetraisopropoxide and an optically active tartrate ester (Scheme 108). Dimethyloxirane can also be used to oxidize sulfides to sulfoxides. 

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