Boron trifluoride-Trifluoroacetic anhydride

A number of Lewis acids have been utilized in the Pomeranz-Fritsch reaction, including polyphosphoric acid and boron trifluoride-trifluoroacetic anhydride. Under the latter conditions yields were best when electron-donating groups were present in the 3- or 3, 4- position of imine 20, whereas unactivated aldehydes failed to cyclise at all. ... 

The Pomeranz-Fritsch method (boron trifluoride + trifluoroacetic anhydride) is not suitable 205 but polyphosphoric acid (PPA) at 100°... 

It has long been apparent that when the acid concentration is too low, the Schiff base is hydrolyzed back to its components and, when it is too high, extensive decomposition results. In order to obviate the decomposition problem, numerous acidic reagents have been tried. Some of these are polyphosphoric acid-phosphorus oxychloride,2 polyphosphoric acid,8 and boron trifluoride-trifluoroacetic anhydride.8 Some improvement has been observed, but many yields are still poor. 

POMERANZ-FRITSCH REACTION Boron trifluoride-Trifluoroacetic anhydride. 

One of the methylthio groups of a ketenedithioacetal is displaced by an anion derived from an active methylene group simultaneously, the other MeS and R (an activating group) are eliminated. A Pomeranz-Fritsch reaction, catalysed by boron trifluoride-trifluoroacetic anhydride (see also Section II. 1), is an attractive synthesis of some l-alkyl-2,3-unsubstituted indoles. Recent work on indoles has been reviewed [3893]. 

An example of an alcohol that can undergo rapid skeletal rearrangement is 3,3-dimethyl-2-phenyl-2-butanol (Eq. 29). Attempts to reduce this alcohol in dichloromethane solution with l-naphthyl(phenyl)methylsilane yield only a mixture of the rearranged elimination products 3,3-dimethyl-2-phenyl-l-butene and 2,3-dimethy 1-3-phenyl-1 -butene when trifluoroacetic acid or methanesulfonic acid is used. Use of a 1 1 triflic acid/triflic anhydride mixture with a 50 mol% excess of the silane gives good yields of the unrearranged reduction product 3,3-dimethyl-2-phenylbutane, but also causes extensive decomposition of the silane.126 In contrast, introduction of boron trifluoride gas into a dichloromethane solution of the alcohol and a 10 mol% excess of the silane... 

Method E To a suspension of 0.67 mM of ruthenium(IV) dioxide dihydrate in 0.8 mL of trifluoroacetic acid, 0.4 mL of trifluoroacetic anhydride, and 4 mL of CH2C12 at 0 C is added, with stirring and under argon, a solution of 0.33 mM of prestegane B in 4mL of CH2C12 and, immediately, 0.2 mL of boron trifluoride-diethyl ether complex. After 3 h. the suspended solid is removed by filtration. Evaporation and flash chromatography affords the pure crystalline product yield 84% mp 228-230°C. 

Dehydration of primary nitroalkanes with phenyl isocyanate or acetic anhydride in the presence of catalytic triethylamine affords nitrile oxides, which may be trapped as their 1,3-dipolar cycloadducts or allowed to dimerize to the corresponding furoxans. Other dehydrating agents that have been used include diketene, sulfuric acid and, when the a-methylene group is activated by electron-withdrawing groups, boron trifluoride in acetic anhydride, trifluoroacetic anhydride with triethylamine, and nitric acid in acetic acid. 

The reaction between o-nitrobenzoic acid and benzene in the presence of trifluoroacetic anhydride and boron trifluoride has been... 

The reaction is acid or base catalyzed. Many catalysts have been tried, including potassium acetate and sodium acetate (27), dimeth-ylformamide (DMF) (28-30), urea ammonium sulfate (29), magnesium perchlorate (31-33), trifluoroacetic acid (32), boron trifluoride (30), sodium acetate (31), potassium hydrogen phosphate (34), and y-rays (35). The best acetylation condition, however, is uncatalyzed acetic anhydride in xylene at 100-130 C (36). 

Bevis, M. J., Forbes, E. J., Naik, N. N., Uff, B. C. Synthesis of isoquinolines, indoles, and benzothiophene by an improved Pomeranz-Fritsch reaction, using boron trifluoride in trifluoroacetic anhydride. Tetrahedron 1971, 27,1253-1259. 

Aryl coupling to a benzylic site has also been observed the monophenol (67) yielded the aryltetralin (68 55%), with thallium trifluoroacetate-boron trifluoride. Probably oxidation to quinone methide precedes the ring closure. Separate oxidation and cyclization steps were employed in the synthesis of ( )-thaliphotphine acetate. ( )-Codamine (69) underwent Wessely oxidation with lead tetraacetate to the acetoxycyclohexadienone (70), which closed in acetic anhydride-acid to ( )-thaliphorphine acetate (71), albeit in modest overall yield (14%). ... 

Esterification Alumina. Boron trifluoride. Diazomethane. Dimethylformamide dimethyl acetal. Dimethylformamide dineopentyl acetal. Dimethyl sulfite. Diphenyidiazomethane. Ethyldicyclohexylamine. Ion-exchange resins. Isobutene. Methanesulfonic anhydride. 3 % Methanolic HCl (see Acetyl chloride). Methyl iodide. l-Methyl-3-p-tolyltriazine. Poly-phosphoric acid. Sulfosalicylic acid. Sulfuryl chloride. p-Toluenesulfonic acid. p-Tpluene-sulfonyl chloride. Triethylamine. Triethylorthoformate. Trifluoroacetic anhydride. Esterification of phosphoric acid Trichloroacetonitrile. 

Oxidation of 5-hydroxyisoquinolines 107a,b,c with LTA in dichloromethane gave the o-quinol acetate 108 which was converted with trifluoroacetic acid to the 3-hydroxyhomoaporphine 109 (64,65). Treatment of o-quinol acetate 111 prepared from 6-hydroxyisoquinoline 110 with acetic anhydride in the presence of an acid (concentrated sulfuric acid, boron trifluoride, or trifluoroacetic acid) gave the 2-hydroxyhomoaporphine 112 (66). 

Carboxylic acid anhydrides or halides normally require the presence of a Lewis acid (often boron trifluoride) for Friedel-Crafts acylation of furans, though trifluoroacetic anhydride will react alone. Aluminium-chloride-catalysed acetylation of furan proceeds 7 x lO times faster at the a-position than at the P-position. 3-Alkyl-furans substitute mainly at C-2 2,5-dialkyl-furans can be acylated at a P-position, but generally with more difficulty. 3-Bromofuran is efficiently acetylated at C-2 using aluminium chloride catalysis. ... 

The following are some further examples. Acetomesitylene is obtained from mesitylene and glacial acetic acid in the presence of phosphoric oxide and kieselguhr, yields reaching 82.5%.525,566 (o-Nitrobenzoyl)mesitylene is obtained (75%) from mesitylene and a-nitrobenzoic acid in the presence of boron trifluoride and trifluoroacetic anhydride.567 Toluene and benzoic acid in the presence of molybdenum pentafluoride give a 70% yield of 4-methylbenzo-phenone, but with aluminum chloride give a mixture of the 2- and the 4-methyl derivative.568... 

The nitration of aromatics is an important chemical reaction, and new reagents include iV-nitropyrazole in the presence of a Lewis acid, metal nitrates in trifluoroacetic anhydride, and silver nitrate-boron trifluoride in acetonitrile. Metal salts, especially cerium(iv) acetate, also promote aromatic nitromethyl-... 

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