Also TFAA

The trifluoromethyl derivative 146 has been obtained as a minor product from the reaction of (l-methyhndol-3-yl)methanol with trifluoroacetic acid anhydride (TFAA), the major product (22% yield) being 6-trifluoromethylindolo[3,2-()]-carbazole [98LTC(B)841]. Several substituted indolo[2,3-()]carbazoles have also been encountered during studies on the reaction of 4,6-dimethoxyindole with... 

Similarly, iV,A/ -dimethyl-3,3 -bisindolylmethane (169) has been used in a related experiment, where treatment thereof with trifluoroacetic fflihydride (TFAA) in diethyl ether at room temperature yielded a mixture of products from which the trifluoromethyl-substituted indolo[3,2-b]carbazole 170 was isolated as the major pentacyclic component, accompanied by the hydroxy derivative 171 as well as small amounts of the indolo[2,3-h]carbazole 146 (Scheme 20). The precursor 169 could also be prepared in situ from A-methylindol-3-methanol under... 

The Jacobsen group has also shown that the recycling of the resin-bounded catalyst can be successfully performed [152,154]. Moreover, they have developed an efficient method for the hydrolysis of the aminonitrile into the corresponding amino acid. This method was apphed for the commercial production of optically active K-amino acids at Rhodia ChiRex (e.g. tert-leucine) the catalyst was immobihsed on a resin support (4 mol %, 10 cycles) and the intermediate hydrocyanation adduct was trapped by simply replacing TFAA with HCOOH/AC2O, for example. Highly crystalhne formamide derivatives were thus obtained in excellent yields (97-98% per cycle) with very high enantioselectivities (92-93% per cycle) [158]. 

Section B of the Scheme 9.1 shows several procedures for the synthesis of ketones. Entry 6 is the synthesis of a symmetrical ketone by carbonylation. Entry 7 illustrates the synthesis of an unsymmetrical ketone by the thexylborane method and also demonstrates the use of a functionalized olefin. Entries 8 to 10 illustrate synthesis of ketones by the cyanide-TFAA method. Entry 11 shows the synthesis of a bicyclic ketone involving intramolecular hydroboration of 1,5-cyclooctadiene. Entry 12 is another ring closure, generating a potential steroid precursor. 

Highly reactive mixed anhydrides can also promote acylation. Phenylacetic acid reacts with alkenes to give 2-tetralones in TFAA-H3P04.55 This reaction involves an intramolecular Friedel-Crafts alkylation subsequent to the acylation. 

Also, Shiraishi et al. [4,5] found that the acylated wood meals prepared by the TFAA and chloride methods are thermally meltable. In addition, the acylated wood samples prepared by the TFAA method show somewhat lower flow temperatures than those prepared by the chloride method. 

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... 

Cyanotrialkylborates (11), which can Iw readily prej red and are stable, are of interest due to their synthetic applicability in organic synthesis. Although no detail introduction of the reactions is n here, a brief account is presented. Cyanotrialkylborates react smoothly with 1 equivalent of trifluoroacetic anhydride (TFAA) at —78 °C and then at room temperature. Oxidation of the intermediates with hydrogen peroxide under basic conditions gives the corresponding symmetrical ketones in excellent yields The reaction is considered to proceed via the reaction path, as indicated in Eq. 23. Unsymmetrical ketones can also be obtained... 

The reactivity of thiazole to nitration has been well reviewed <1984CFIEC(6)235>. Recently, nitration at C-4 of 2,5-dimethylthiazole 62 was accomplished with trifluoroacetic anhydride (TFAA) and fuming nitric acid at —15°C as shown in Scheme 9 to give the product 63 in 67% yield <2005ARK179>. The nitration of thiazole itself was not studied in this work due to poor solubility under the reaction conditions <2005ARK179>. See also Section 4.06.7.2. 

Trifluoroacetic anhydride (TFAA) is also a very potent activator for DMSO and concomitant trifluoroacetylation of the starting alcohol is usually not observed [27]. Both the Swem and the TFAA procedure are carried out at low temperature to prevent undesired side reactions, particularly formation of the methylthiomethyl ether. Before these two methods became developed, acetic anhydride was often used for DMSO activation. Flowever, the oxidation under these conditions is slower and the methylthiomethyl ether byproduct is often observed [27]. 

A useful alternative to the carbonylation route to ketones and trialkylmethanols from alkylboranes is the cyanidation reaction. The nitrile anion [(-) C=N ] is isoelectronic with CO and also reacts with R3B. However, the cyanoborate salts are thermally stable and therefore require an electrophile such as benzoyl chloride or trifluoroacetic anhydride (TFAA) to induce 1,2-migration. 

The reaction of alcohol (41) with TFAA, followed by treatment with sodium azide, gave (42) in 75% overall yield. The p-toluenesulfonate or methanesulfonate of (41) has also been demonstrated to react with sodium azide affording (42) but in lower yield. Deprotection and subsequent reduction with hydrogen sulfide gave amine (43 Scheme 19). ... 

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