Selective acetylations acetic anhydride

Acetylsucrose [63648-81-7] has been prepared in 40% yield by direct acetylation of sucrose using acetic anhydride in pyridine at 40° C (36). The 6-ester has subsequently been obtained in greater than 90% yield, by way of 4,6-cycHc orthoacetate. Other selective methods for the 6-acylated derivatives include the use of alkyl tin reagents such as dibutyl tin oxide (37) and of dibutyl stannolane derivatives (38). Selective acetylation of sucrose by an enzymic process has also been described. Treatment of sucrose with isopropenyl acetate in pyridine in the presence of Lipase P Amano gave, after chromatography, 6-0-acetylsucrose (33%) and 4/6-di-O-acetylsucrose (8%). The latter compound has been obtained in 47% yield by the prolonged treatment (39). 

Whereas treatment of ( )-29 with camphanic chloride achieves the selective esterification of the hindered C-9 hydroxyl group, the action of acetic anhydride on (+)- 29 results in the equally selective acetylation of the C-10 hydroxyl group It is not clear to what this discrepancy should be attributed, so we will not offer a rationalization here. This unexpected result is, however, most gratifying because TPAP-NMO oxidation27 of the remaining C-9 hydroxyl furnishes keto acetate 6 (88 % overall yield). You will note that the contiguous keto and acetate functions in 6 are both expressed in the natural product. 

The monoacetate 9a (R1 = Ac) and the diacetate 10a (R1 = R2 = Ac) are obtained by treatment of 8 with acetic anhydride in anhydrous pyridine at room temperature 4 the oxo group in position 5 of 8 is more reactive towards acetylation. Similarly, the S,S-dioxidc of 8 can be converted to the bisacetylated S,5-dioxide of 10a in 78 % yield.74 Methylation of 8 with diazomethane gives 9c (65 % yield), along with 14 % of the 3-methoxy compound 11. Other alkylation agents, such as dimethyl sulfate in the presence of potassium carbonate, selectively give 9c, albeit in lower (30 %) yield.90 The dimethyl enol ether 10c (R1 = R2 = Me) is obtained by a subsequent methylation of 9c (R1 = Me) with dimethyl sulfate and potassium teri-butoxide.90... 

Another patent apphcation (28) describes the use of zeolite/TUD-1 with optionally a metal function for a variety of reactions. In an example, as-synthesized MCM-22 / TUD-1 was tested for acylation of 2-methoxynaphthalene with acetic anhydride to 2-acetyl-6-methoxynaphthalene at 240°C. After reaction for six hours, conversion of 2-methoxynaphthalene reached 56% with 100% selectivity to 2-acetyl-6-methoxynaphthalene. Other zeolite catalysts were similarly tested, but none were nearly as effective. 

Reduction of Methylene Violet with zinc in acetic acid gives the air-sensitive leuco 20 which is further reacted with acetic anhydride in mild conditions to yield the acetylated leuco 21. The latter being air stable can be isolated and, the ring N-H being less reactive is not affected by acetylation at room temperature. The leuco 21 is again aroylated to produce the leuco 22. Selective hydrolysis provides the desired leuco dye 12 which regenerates the true Methylene Violet (6) on oxidation.83... 

Selective replacement of hydroxyl groups by bromine has been reported for some inositols and inosamines. DL-2-Amino-2-deoxy-epi-inositol hydrochloride plus acetyl bromide in acetic anhydride gave, after 6 hours at 150°, DL-4-acetamido-l,2,6-tri-0-acetyl-3,5-dibromo-3,4,5-trideoxy-c/uro-inositol in 32% yield, the bromine atoms having been introduced with inversion.407 Under related conditions, DL-epi-... 

It has been demonstrated that organotin-mediated multiple carbohydrate esterifications can be controlled by the acytaring reagent and the solvent polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas when acetic anhydride is employed, kinetic control takes place. Very good selectivity can furthermore be obtained in more polar solvents. These results can be used in the efficient preparation of prototype carbohydrate structures. 

Treatment of the ammonium salt of 3,5-dinitro-1,2,4-triazole (113) with hydrazine hydrate leads to selective reduction of one of the nitro groups to yield 3-amino-5-nitro-1,2,4-triazole (ANTA) (114), a high performance explosive (calculated VOD 8460 m/s) possessing thermal stability (m.p. 238 °C) and an extremely low sensitivity to impact. ANTA (114) is also synthesized from the nitration of 3-acetyl-l,2,4-triazole with anhydrous nitric acid in acetic anhydride at subambient temperature followed by hydrolysis of the acetyl functionality. The ammonium salt of 3,5-dinitro-l,2,4-triazole (113) is itself a useful explosive which forms a eutectic with ammonium nitrate. ... 

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%. 

The association between acetylcholine levels and Alzheimer s disease, as noted more than once previously, has led to the search for novel compounds that raise the level of that neurotransmitter by inhibiting acetylcholinesterase, the agent of its inactivation. The benzisoxazole icopezil (60-8) has undergone several trials against that debilitating disease as a result of selective chohnesterase inhibiting activity in the CNS. Friedel-Crafts acylation of the indolone (60-1) with acetyl chloride affords the methyl ketone (60-2). This is then converted to its oxime and that function acylated with acetic anhydride to yield (60-3). Treatment with pyridinium perbromide... 

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