Acetic anhydride-Methanesulfonic acid

Compound 102 is used as the building block for the syntheses of PNU-86093 and its analogues, as described in Scheme 21. Namely, the Friedel-Crafts acetylation reaction of 102 under acetic anhydride, methanesulfonic acid, and methanesulfonyl anhydride [51,65] affords compound 103 (PNU-... 

PUMMERER REARRANGEMENT Acetic anhydride-Methanesulfonic acid. Acetic anhydride-Sodium acetate. 

Table 3.10 Kinetic data for acetolysis of pennethylated methyl glycopyranosides of D-glucose, D-galactose, and D-mannose (111-116) with acetic anhydride-methanesulfonic acid (30 1 v/v) at 75 °C...

The 4-amino group of 31 was selectively acetylated under acidic conditions using acetic anhydride (1 equiv.) and methanesulfonic acid (1 equiv.) in acetic acid and f-butylmethyl ether to give 32. Deallylation of 32 using 10% Pd/C in the presence of ethanolamine in refluxing ethanol proceeded as before to afford 1, which was converted to the phosphate salt in 70% yield with high purity (99.7%). The overall yield of 1 from epoxide 23 was 35-38%. 

Other useful dehydrating agents are dimethylaminosulfur trifluoride (DAST), methyl A -(triethylammoniosulfonyl)carbamate (Burgess salt), acetic anhydride, oxalyl chloride, and phosphorous oxychloride, each one in combination with triethylamine (89). Dehydration of O-sUylated hydroxamic acids using trifluoro-methanesulfonic anhydride and triethylamine under mild conditions also gave nitrile oxides, which in the presence of olefins led to the formation of 2-isoxazolines in moderate to good yields (90). In view of the less readily available starting materials, this method probably will be of limited use. 

Pyrrole- and indole-carboxylic acid chlorides react with dialkyl- and diaryl-cadmium to yield the ketones and it is noteworthy that the reaction of the anhydride of indole-2,3-dicarboxylic acid with diphenylcadmium produces 3-benzoylindole-2-carboxylic acid and not its isomer (53JCS1889). The ability of l-methylindole-2-carboxylic acid to react with nucleophiles is enhanced by conversion into the mixed anhydride with methanesulfonic acid. The mixed anhydride reacts with carbanions derived from diethyl malonate and from methyl acetate to yield the indolyl (3- keto esters (80TL1957). 

The preparation of yet another variant on the theme starts with quina-zolone (155). Treatmment with methanesulfonic acid selectively cleaves the ether at the more electron-rich position to give the phenol (156). This functional group is then acylated by means of acetic anhydride... 

For lab prepns, and occasionally in industrial use, more expensive nitrating agents may be employed, as for example solns of nitric acid in inert organic solvents (chlf, carbon tetrachloride, eth, nitromethane, etc), or a soln of nitric acid in phosphoric or acetic acids or in acetic anhydride, trifluoroacetic anhydride or trifluoro-methanesulfonic acid (Ref 94)... 

Reaction of 2-phenylsulfinyl esters such as (133) with acetic anhydride is slow at room temperature, but when a catalytic amount of methanesulfonic acid is present in the reaction medium, conversion to the vinyl sulfide (134) is complete after a few hours at 20-40 C (Scheme 31). Mixtures of ( )/(2) isomers are usually obtained, with the (2)-isomer generally being the more stable. These isomers are in-terconverted on heating, a process which occurs slowly on standing, even in the dark. The discovery that photochemical or free radical induced 1,3-shift of the PhS group in (135) to the y-position can be effected offers an additional opportunity to modulate the a/y selectivity in the extended enolate chemistry of a,3-unsaturated carbonyl systems. 

Isoindoles can be produced by eliminations from A-substituted isoindolines (1,3-dihydro-isoindoles), themselves readily produced by the reaction of a nitrogen nucleophile and a l,2-bis(bromomethyl)-benzene examples are the pyrolytic eUmination of acetic acid from the cyclic hydroxylamine acetate,or, at a much lower temperature, of benzyl alcohol from an A-hydroxy-isoindoline benzyl ether, or of methanesulfonic acid from a corresponding mesylate. A-substituted isoindoles, too, have generally been made from an isoindoline by elimination processes, thus A-oxides can be made to lose water by pyrolysis," or better, by treatment with acetic anhydride. ... 

Pummerer rearrangement (5,3-4). 2-Phenylsulfonyl ketones (1) can be converted into (2) by a Pummerer rearrangement using acetic anhydride and a catalytic amount of methanesulfonic acid in CH2CI2 at 20°. The rearrangement provides a general synthesis of a-phenylthio-a, -unsaturated ketones (2). 

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