Trichloroacetic anhydride

Aldehydes can be converted to acylals by treatment with an anhydride in the presence of BF3, other Lewis acids, proton acids, or PCI3. The reaction cannot normally be applied to ketones, though an exception has been reported when the reagent is trichloroacetic anhydride, which gives acylals with ketones without a catalyst. ... 

This methodology has also been used by Bose, who described the synthesis of the thienamycin side chain [119], the first step of which was a [2+2] cycloaddition under microwave irradiation. Likewise, Khajavi described the reaction of trichloroacetic anhydride with imines [120] with classical heating the reaction requires the use of Fe2(CO)9 as a catalyst, whereas under microwave irradiation a catalyst is not required. 

Kusumoto and coworkers have found that the treatment of hemiacetal 1 with trifluoro- or trichloroacetic anhydride 94 (1 equiv) and trimethylsilyl perchlorate (0.2 equiv) selectively provides the corresponding anomeric ester intermediate 91 [152], Hemiacetal acylation occurs even in the presence of the alcohol acceptor. With Lewis acid assistance, the glycosyl ester intermediate is displaced to provide disaccharide products in good yields. This transformation allowed the synthesis of disaccharides 98 (81%) and 99 (91%). In some cases, acetic anhydride has been used as the electrophilic activator of hemiacetal donors and the reaction with thiol acceptors yields S-linked glycosides [153,154],... 

Representative Procedure for Carbonyl Promoted Clycosylation with Cl-Hemiacetal Donors Using Trichloroacetic Anhydride [152]... 

Diastereomeric menthyl arenesulfinates as well as enantiomeric alkyl alkanesulfinates racemize in the presence of trichloroacetic anhydride even at room temperature (278). A mechanism based on kinetic investigations was proposed in which the formation of alkoxyacyloxysulfonium salt is the rate-determining step. 

Atta-ur-Rahman et al. reported the oxidation of catharanthine by a modified Prevost reaction to result in formation of the 20-a-acetoxy derivative. Coupling of its A-oxide (77) to vindoline, using trichloroacetic anhydride (rather than the usual trifluoro compound), and subsequent re-... 

Schiff bases 293 and 295 prepared from 2-aminoquinoline and 1-aminoisoquinoline with aromatic aldehydes reacted with trichloroacetic anhydride in boiling xylene to afford 2-chloro-3-phenyl-l//-primido[l,2-a]quinolin-l-one (294) and 3-chloro-2-aryl-4//-pyrimido[2,l-a]isoquinolin-4-ones (296) (77CPB1607). 

For trace analysis it is common to include in a derivatization step the formation of a derivative that not only aids the desired chromatographic or separation factors, but also provides sensitivity to one or another of the specific detectors available. It is common to use a halogen-substituted derivatizing reagent to provide simultaneously decreased polarity or reactivity, better chromatographic separation, and more selective, sensitive detection using electron capture. Thus, for example, trichloroacetic anhydride is used to form acetate derivatives instead of using acetic anhydride. 

According to Morimoto and Sekiya,170,171 in boiling toluene the Schiff bases (111) and trichloroacetic anhydride yield 2-aryl-3-chloro-4-oxo-pyrido[l,2-a]pyrimidines (112). 

Dihydropyridines substituted at the 3- and/or 4-positions undergo selective acylation with trichloroacetic anhydride to give 5-trichloroacetyl-l,4-dihydropyridines 136, which are easily converted by the haloform reaction to esters 137 (Scheme 37) <1998TL9275, 2002T8099, 2003TL4711>. Hydrogenation, over platinum oxide, of... 

The scope of the reaction is quite general, allowing reasonable variation for each component. Apart from TFAA, substituted difluoroanhydrides also react, yielding the expected derivatives with diverse groups attached to the exocyclic carbonyl moiety. Chlorinated anhydrides are less reactive and only trichloroacetic anhydride (TCAA) leads to dipole 251 in moderate yield (Scheme 38). A new... 

Dimethyl sulfoxlde-Oxalyl chloride, 192 Dimethyl sulfoxide-3-Sulfopropanoic anhydride complex, 192 Dimethyl sulfoxide-Trichloroacetic anhydride, 192... 

A further route to compounds with an aromatic ring A lies in an unusual acid-catalysed rearrangement of steroidal A -3-ketones. Testosterone (35) is reported to give the 4-methyl aromatic compound (36) with trichloroacetic anhydride in the presence of toluene- -sulphonic acid [178]. The mechanism of this reaction is not clear. 

Explain why trichloroacetic anhydride [(Cl3CC0)20] is more reactive than acetic anhydride [(CH3C0)20] in nucleophilic acyl substitution reactions. 

The biomimetic total synthesis of (+)-20-epiervatamine was accomplished by J. Bosch et al. The authors used the addition of 2-acetylindole enolate to a 3-acylpyridinium salt as akey step to connect the two main fragments. The in situ formed 1,4-dihydropyridine was trapped with trichloroacetic anhydride to afford the corresponding trichloroacetyl-substituted 1,4-dihydropyridine derivative. The conversion of the trichloroacetyl group to a methyl ester was achieved by treatment with sodium methoxide. This transformation can be regarded as the second step of the haloform reaction. 

From a TBDMS or TIPS ether trichloroacetic anhydride, 3HF-TEA, 80 C, 2 h, 90-93% yield.3... 

Anhydrides may also be employed instead of an acid chloride. The mixed anhydride of acetic and formic acid reacts with 1-iV-morpholinocyclohexene to give 2-hydro-xymethylenecyclohexanone . Acylation of isobutyraldehyde enamines with trichloroacetic anhydride in tetrahydrofuran at room temperature gives the a-trichloromethyl-j5-trichloroacetyl adduct . This occurs by initial ) -acylation to give the acyl iminium trichloroacetate, followed by decarboxylation and nucleophilic addition of the tri-chloromethyl anion to the iminium group. Trifluoroacetic anhydride under the same conditions just gave the -trifluoroacetyl derivative . 

A fused 5-chloropyrimidin-4-one ring is formed from an imine and ring-nitrogen by heating with either trichloroacetic anhydride in boiling toluene... 

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