Trifluoroacetic Anhydride oxidation

Very few reports of competitive reactions of alcohols have appeared in activated dimethyl sulfoxide oxidations, but the results obtained from these limited studies are interesting. It is known that dimethyl sulfoxide-trifluoroacetic anhydride oxidation is selective for primary or secondary alcohols in the presence of benzylic or allylic alcohols, due to the latter alcohols being preferentially converted to trifiu-oroacetates. Additionally, secondary alcohols are known to be more reactive than primary alcohols in these oxidations, although the measured rate differences are not very high and selectivity cannot be guaranteed. 

The o-nitrobenzyl and p-nitrobenzyl ethers can b prepared and cleaved by many of the methods described for benzyl ethers. The p-nitrobenzyl ether is also prepared from an alcohol and p-nitrobenzyl alcohol (trifluoroacetic anhydride, 2,6-lutidine, CH2CI2, 67% yield). In addition, the o-nitrobenzyl ether can be cleaved by irradiation (320 nm, 10 min, quant, yield of carbohydrate " 280 nm, 95% yield of nucleotide ). The p-nitrobenzyl ether has been cleaved by electrolytic reduction (—1.1 V, DMF, R4N X, 60% yield) and by reduction with Na2S204 (pH 8-9, 80-95% yield). These ethers can also be cleaved oxidatively (DDQ or electrolysis) after reduction to the aniline derivative. ... 

A very common oxidizing reagent is peroxytrifluoroacetic acid, which is usually generated in situ from trifluoroacetic acid [29, 30, 31] or trifluoroacetic anhydride [32, 33, 34] and hydrogen peroxide Peroxytrifluoroacetic acid is one of the most efficient epoxidizing reagents [35] It can be used to prepare epoxides... 

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)... 

When 2-lithio-2-(trimethylsilyl)-l,3-dithiane,9 formed by deprotonation of 9 with an alkyllithium base, is combined with iodide 8, the desired carbon-carbon bond forming reaction takes place smoothly and gives intermediate 7 in 70-80% yield (Scheme 2). Treatment of 7 with lithium diisopropylamide (LDA) results in the formation of a lactam enolate which is subsequently employed in an intermolecular aldol condensation with acetaldehyde (6). The union of intermediates 6 and 7 in this manner provides a 1 1 mixture of diastereomeric trans aldol adducts 16 and 17, epimeric at C-8, in 97 % total yield. Although stereochemical assignments could be made for both aldol isomers, the development of an alternative, more stereoselective route for the synthesis of the desired aldol adduct (16) was pursued. Thus, enolization of /Mactam 7 with LDA, as before, followed by acylation of the lactam enolate carbon atom with A-acetylimidazole, provides intermediate 18 in 82% yield. Alternatively, intermediate 18 could be prepared in 88% yield, through oxidation of the 1 1 mixture of diastereomeric aldol adducts 16 and 17 with trifluoroacetic anhydride (TFAA) in... 

Several alternative procedures have been developed in which other reagents replace carbon monoxide as the migration terminus.11 The most generally applicable of these methods involves the use of cyanide ion and trifluoroacetic anhydride (TFAA). In this reaction the borane initially forms an adduct with cyanide ion. The migration is induced by N-acylation of the cyano group by TFAA. Oxidation and hydrolysis then give a ketone. 

Preparatively useful procedures based on acetic anhydride,25 trifluoroacetic anhydride,26 and oxalyl chloride27 have been developed. The last method, known as the Swern oxidation, is currently the most popular. 

The spirobenzylisoquinoline 171b derived from berberine (15) (Section IV,A,1) was oxidized with m-chloroperbenzoic acid to the /V-oxide 389, which was treated with trifluoroacetic anhydride to afford dehydrohydrastine (370) in 56% overall yield (Scheme 71) through the Polonovski reaction (187). Holland et al. (188,189) reported the reverse reaction from dehydrophthalides to spirobenzylisoquinolines, namely, 370 was reduced with diisobutylalu-minum hydride to give a mixture of two diastereoisomeric spirobenzylisoquinolines 320 and 348 via the enol aldehyde. This reaction was applied to synthesis of various spirobenzylisoquinoline alkaloids such as (+)-sibiricine (352), ( + )-corydaine (347), (+ )-raddeanone (354), ( )-yenhusomidine (359), (+ )-ochrobirine (343), and ( )-yenhusomine (323). 

The differing nucleophilicity of acetate and trifluoroacetate anion determines the direction in which naphtho[l,8-b,c]-l,5-dithiocine-l-oxide 59 rearranges on treatment with acetic and trifluoroacetic anhydrides. In both cases the reaction proceeds through formation of a disulfonium dication, but the final products are different. When acetic anhydride is used, the reaction affords the corresponding a-acetylsulfide 60 - a normal product of the Pummerer rearrangement, while trifluoroacetic anhydride causes isomerization with formation of dithioacetal 61 (Scheme 22).87... 

Laboratory transformations took advantage of fragmentation of dregamine (30), tabemaemontanine (31), and vobasine (32) as N4 oxide induced by treatment with trifluoroacetic anhydride (Polonovski-Potier reaction) (192) and reductive capture of the intermediate iminium ion (Scheme 1). 

Utilizing Wenkert s cyclization process, a number of new approaches have been elaborated for the synthesis of simple indolo[2,3-a]quinolizine derivatives. For example, treatment of JV-[2-(indol-3-yl)ethyl]piperidine (V-oxide (134) with trifluoroacetic anhydride gave piperideinium intermediate 135 in a Polonovski-type reaction, which could be cyclized in acidic medium to ( )-l (101). 

Boron-Wittig reaction (12, 12-13). The direct reaction of the anion of an alkyldimesitylborane at -78° with an aromatic aldehyde followed by oxidation results in an (E)-alkene in low yield. The intermediate adduct can be isolated in about 80% yield as the silyl ether of a iyn-l,2-diol by addition of CISi(CH,), to the reaction, and this product on desilylation (HF, CHjCN) affords (E)-alkenes with high selectivity. Somewhat lower (E)-selectivity obtains in a one-pot reaction. In contrast, addition of trifluoroacetic anhydride (slight excess) to the reaction at -78° to -110° results in a (Z)-alkene with almost comparable selectivity (Z/E 9 1). 

Several laboratories have reported that Swern oxidation of alcohols can be accompanied of a-chlorination of keto or (1-keto ester groups. Undesired electrophilic chlorination can be avoided by use of oxalyl chloride (1.05 equiv.) and DMSO (2.5 equiv.) in stoichiometric amounts or by use of acetic anhydride or trifluoroacetic anhydride in place of oxalyl chloride.1... 

Treatment of 2-methylpyridine A -oxide with trifluoroacetic anhydride gives rise to 2-hydroxymethylpyridine. 

Mixed anhydrides such as benzenetellurinyl acetate (PhTe(O)OAc), benzenetellurinyl trifluoroacetate (PhTe(0)OCOCF3) and benzenetellurinyl trifluoromethanesulphonate (PhTe(0)0S02CF3), prepared by reacting benzenetellurinic anhydride with acetic anhydride, trifluoroacetic anhydride and trifluoromethane-sulphonic anhydride, respectively, have been recognized as valuable oxidizing reagents, in some cases superior to the parent benzenetellurinic anhydrides. ... 

A coupling of vindoline (3) with catharanthine A-oxide (45), mediated by trifluoroacetic anhydride, and subsequent reduction with sodium boro-hydride delivered anhydrovinblastine (42) in up to 40% yield, accompanied by minor amounts of the undesired C-16 (R) isomer 24 as well as some 17-deacetylanhydrovinblastine (46) (Scheme 13) (38-41). The struc-... 

The relatively facile formation of anhydrovinblastine (42) by the modified Polonovski reaction, and the poor yields experienced on coupling of other catharanthine derivatives, made anhydrovinblastine an attractive precursor for the preparation of additional binary alkaloids, including vinblastine itself (50,57). Hydrogenation to 20 -deoxyleurosidine (61a), formation of its Af -oxide (78), and reaction with trifluoroacetic anhydride led to the enamine 59 (Scheme 23). Oxidation of this enamine with thal-... 

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