Trifluoroacetic anhydride catalyst

Furan can also be acylated by the Vilsmeier-Haack method. Acylation of furans can also be carried out with acid anhydrides and acyl halides in the presence of Friedel-Crafts catalysts (BF3-Et20, SnCU or H3PO4). Reactive anhydrides such as trifluoroacetic anhydride, however, require no catalyst. Acetylation with acetyl p-toluenesulfonate gives high yields. 

Activating agents, such as trifluoroacetic anhydride 1,1 -carbonyldiimidazolc carbodiimides sulfonyl, tosyl, and picryl chlorides and a range of phosphorus derivatives can promote direct solution reactions between dicarboxylic acids and diols or diphenols in mild conditions. The activating agents are consumed during the reaction and, therefore, do not act as catalysts. These so-called direct polycondensation or activation polycondensation reactions proceed via the in situ transformation of one of the reactants, generally the carboxylic acid, into a more... 

Trifluoroacetic anhydride, which activates the polyesterification of 4-hy-droxybenzoic acid via the formation of a mixed anhydride,307 and 1,1 -carbonyldiimidazole308 were the first reported activating agents. The reaction between 1,1 -carbonyldiimidazolc and carboxylic acids proceeds through the formation of N-acylimidazolcs, which react with aliphatic diols in the presence of sodium ethoxide catalyst (Scheme 2.28). 

Entry 5 is an example of nitration in acetic anhydride. An interesting aspect of this reaction is its high selectivity for the ortho position. Entry 6 is an example of the use of trifluoroacetic anhydride. Entry 7 illustrates the use of a zeolite catalyst with improved para selectivity. With mixed sulfuric and nitric acids, this reaction gives a 1.8 1 para ortho ratio. Entry 8 involves nitration using a lanthanide catalyst, whereas Entry 9 illustrates catalysis by Sc(03SCF3)3. Entry 10 shows nitration done directly with N02+BF4, and Entry 11 is also a transfer nitration. Entry 12 is an example of the use of the N02—03 nitration method. 

The general picture emerging is that acid chlorides are sufficiently electrophilic to N-acylate carbazole directly but that acid anhydrides require a Lewis acid or protonic acid catalyst. Direct and efficient N-trifluoroacetyla-tion with trifluoroacetic anhydride nicely illustrates the balance, this more reactive anhydride requiring no catalyst. ... 

Detection in liquid chromatography is mostly performed by fluorescence and/or ultraviolet absorption. In a few instances, electrochemical detection has also been employed (357, 368). For compounds that exhibit inherent intense fluorescence such as albendazole and metabolites (319, 320, 338, 355), closantel (344), and thiabendazole and metabolites (378), fluorometric detection is the preferred detection mode since it allows higher sensitivity. Compounds that do not fluoresce such as eprinomectin, moxidectin, and ivermectin, are usually converted to fluorescent derivatives prior to their injection into the liquid chromatographic analytical column. The derivatization procedure commonly applied for this group of compounds includes reaction with trifluoroacetic anhydride in presence of A-methylimidazole as a base catalyst in acetonitrile (346, 347, 351, 352, 366, 369, 372-374). The formation of the fluorophore is achieved in 30 s at 25 C and results in a very stable derivative of ivermectin and moxidectin (353) but a relatively unstable derivative of eprinomectin (365). However, the derivatized extracts are not pure enough, so that their injection dramatically shortens the life of the liquid chromatographic column unless a silica solid-phase extraction cleanup is finally applied. 

The acylation of alkenes with trifluoroacetic anhydride having only weak elec-trophilicity was reported to give a,p-unsaturated ketones in 19-49% yields.117 118 The reaction requires the use of the Me2S—BF3 complex as catalyst and takes place only with alkenes that readily form stable carbocations. Alkenes were also electrolyzed in CH2C12 solution of Et4NCl as the electrolyte at —5 to — 10°C in the... 

Sigman and Jacobsen reported the first example of a metal-catalyzed enantioselective Strecker-type reaction using a chiral Alnl-salen complex (salen = N,N -bis(salicyhdene)-ethylenediamine dianion) [4]. A variety of N-allylimines 4 were evaluated in the reaction catalyzed by complex 5 to give products 6, which were isolated as trifluoroacetamides in good yields and moderate-to-excellent enantioselectivities (Scheme 3). Substituted arylimines 4 were the best substrates, while alkyl-substituted imines afforded products with considerably lower ee values. Jacobsen and co-workers also reported that non-metal Schiff base catalysts 8 and 9 proved to be effective in the Strecker reaction of imines 7 with hydrogen cyanide to afford trifluoroacetamides 10 after reaction with trifluoroacetic anhydride, since the free amines were not stable to chromatography (Scheme 4) [5]. 

Scheme 3. Asymmetric Strecker synthesis with chiral Alm-Salen catalyst 5 (Sigman and Jacobsen). TFAA = trifluoroacetic anhydride.

Trifluoroacetylation142,143,143a by trifluoroacetic anhydride in an inert solvent has proved to be particularly suitable for such studies of comparative reactivity. Trifluoroacetic anhydride is, in fact, able to acylate reactive aromatic substrates in the absence of any added Friedel-Crafts catalyst,144 a circumstance which avoids the above-mentioned complications arising from the interactions of many heterocycles with such catalysts.139... 

Attempted dehydration using an acid catalyst or iodine failed, giving mainly acetophenone. When acetic anhydride is employed instead of trifluoroacetic anhydride, the reaction proceeds very slowly. Dehydration with excess methanesulfonyl chloride and trlethylamine gives the product in high yield however, the distilled product has a strong odor of sulfur compound. 

The early work was done with acetyl chloride catalyzed with lead acetate [2], propionic and butyric anhydrides in xylene without catalyst [49], and several unsaturated carboxylic acids in the presence of trifluoroacetic anhydride (TFAA) [62,63]. 

Marshall et al. reported that more reactive allyltin analogs can be used instead of allylsilane nucleophiles in our CAB 1 catalyst system, and found that trifluoroacetic anhydride is an efficient promoter that retains stereoselectivity (Eq. 67) [50aj. 

The maiin domain of oxidation with dimethyl sulfoxide is the conver-sionofprimary alcoholsinto aldehydes andofsecondaryalcoholsintoketones. These reactions are accomplished under very mild conditions, sometimes at temperatures well below 0 °C. The reactions require the presence of acid catalysts such as acetic anhydride [713, 1008, 1009], trifluoroacetic acid [1010], trifluoroacetic anhydride [1011, 1012, 1013], trifluorometh-anesulfonic acid [1014], phosphoric acid [1015, 1016], phosphorus pentox-ide [1006, 1017], hydrobromic acid [1001], sulfur trioxide [1018], chlorine [1019, 1020], A -bromosuccinimide [997], carbonyl chloride (phosgene) [1021], and oxalyl chloride (the Swem oxidation) [1022, 1023, 1024], Dimethyl sulfoxide also converts sufficiently reactive halogen derivatives. into aldehydes or ketones [998, 999] and epoxides to a-hydroxy ketones at -78 °C [1014]. 

Vinyl sulfides are prepared from sulfoxides under a variety of conditions. These include reaction with acetic anhydride at reflux, with trifluoroacetic anhydride in the presence of an amine base and with acetic anhydride in the presence of an acid catalyst. In fact, precautions must be taken in certain Pum-merer reactions discussed in the preceding sections to avoid competing vinyl sulfide formation. 

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