Acetic anhydride with sulfoxides

Transformations of Methyl 5-0-Benzyl-2-0-methyl-/3-I)-glueofuranosidurono-6,3-lae-tone (86) to Dimethyl (Z,E)-2-Methoxy-5-(phenylmethoxy)-2,4-hexadienedioatevl (87). ( Elimination employing DBU b oxidation with silver oxide-sodium hydroxide followed by diazomethane esterification c acidic glycoside cleavage, oxidation by dimethyl sulfoxide-acetic anhydride with formation of 5-0-benzyl-2-0-methyI-D-glucaro-1,4 6,3-dilactone, elimination by using DBU, followed by short treatment with diazomethane d elimination by DBU with subsequent diazomethane esterification e sodium borohydride in hexamethylphosphoric triamide 1 catalytic oxidation followed by short treatment with diazomethane " dimethyl sulfoxide-sulfur trioxide-pyridine-triethylamine.150)... 

A different semisynthetic method involves the acylation of an amino alcohol with a peptide ester and the resulting amino alcohol is subsequently oxidized to the aldehyde 40 The acylation of H-Phe[CH2OH] with the peptide ester Z-Ala-Ala-Leu-OMe is carried out in 5% DMF/MeCN with the subtilisin distributed on the surface of macroporous silica gel. The resulting peptide alcohol is oxidized under mild conditions using anhydrous dimethyl sulfoxide and 20-fold excess of acetic anhydride with purification via flash chromatography 40] Z-Phe[CH2OH] has been oxidized under these conditions and the optical rotation indicates little epimerization as compared to literature values 11 40 ... 

Low DS starch acetates ate manufactured by treatment of native starch with acetic acid or acetic anhydride, either alone or in pyridine or aqueous alkaline solution. Dimethyl sulfoxide may be used as a cosolvent with acetic anhydride to make low DS starch acetates ketene or vinyl acetate have also been employed. Commercially, acetic anhydride-aqueous alkaU is employed at pH 7—11 and room temperature to give a DS of 0.5. High DS starch acetates ate prepared by the methods previously detailed for low DS acetates, but with longer reaction time. 

The initiating step in these reactions is the attachment of a group to the sulfoxide oxygen to produce an activated intermediate (5). Suitable groups are proton, acyl, alkyl, or almost any of the groups that also initiate the oxidations of alcohols with DMSO (40,48). In a reaction, eg, the one between DMSO and acetic anhydride, the second step is removal of a proton from an a-carbon to give an yUde (6). Release of an acetate ion generates the sulfur-stabilized carbonium ion (7), and the addition of acetate ion to the carbonium ion (7) results in the product (eq. 15) ... 

Cellulose dissolved in suitable solvents, however, can be acetylated in a totally homogeneous manner, and several such methods have been suggested. Treatment in dimethyl sulfoxide (DMSO) with paraformaldehyde gives a soluble methylol derivative that reacts with glacial acetic acid, acetic anhydride, or acetyl chloride to form the acetate (63). The maximum degree of substitution obtained by this method is 2.0 some oxidation also occurs. Similarly, cellulose can be acetylated in solution with dimethylacetamide—paraformaldehyde and dimethylformamide-paraformaldehyde with a potassium acetate catalyst (64) to provide an almost quantitative yield of hydroxymethylceUulose acetate. 

Thermolysis of trithiane (69) or carbonate (70) at reduced pressure yields methylene-thiirane which is stable in cold, dilute solution (Scheme 152) (78JA7436, 78RTC214). A novel acenaphthylene episulfide is obtained by treatment of the six-membered sulfoxide (71) with acetic anhydride (Scheme 153) (68JA1676), and photolysis of (72) gives a low yield of episulfide (73 Scheme 154) (72JA521). Low yields may be due to the desulfurization of the thiiranes under the reaction conditions. 

Vicinal glycols may be oxidized to the corresponding 17a-hydroxy-20-ketones in reasonable yields by means of chromium trioxide in dimethylfor-mamide in the presence of manganese dichloride, or by treatment with dimethyl sulfoxide-acetic anhydride. ... 

Fortunately, the oxidation of l,2 5,6-di-0-isopropylidene-a-D-glucofura-nose to l,2 5,6-di-0-isopropylidene-a-D-nfoo-hexofuranos-3-ulose (1) can be accomplished using either phosphorus pentoxide (10, 44) or acetic anhydride (10, 52) in methyl sulfoxide although this oxidation is effected with ruthenium tetroxide (6,7, 46), it is exceeding difficult with other oxidizing agents (53). Keto-sugar 1 is reduced stereospecifically... 

The crystalline phenylboronate derived by similar treatment of methyl a-L-fucopyranoside was shown to possess the 3,4-cyclic structure (25). This assignment is based on oxidation of compound 25 with methyl sulfoxide-acetic anhydride and the chromatographic identification of... 

Due to their thermal instability, this method cannot be applied to the preparation of benzo-thiepins. Although the ft-oxo sulfoxide moiety in precursors such as 5-methoxy-4-phenyl-l-benzothiepin-3(2/7)-one 1-oxide makes them candidates for a Pummerer reaction, treatment with acetic anhydride and triethylamine at - 30 C results in preferential enol acetylation to afford the corresponding 1-benzothiepin 1-oxide.14... 

The Pummerer reaction346 of conformationally rigid 4-aryl-substituted thiane oxides with acetic anhydride was either stereoselective or stereospecific, and the rearrangement is mainly intermolecular, while the rate-determining step appears to be the E2 1,2-elimination of acetic acid from the acetoxysulfonium intermediates formed in the initial acetylation of the sulfoxide. The thermodynamically controlled product is the axial acetoxy isomer, while the kinetically controlled product is the equatorial isomer that is preferentially formed due to the facile access of the acetate to the equatorial position347. The overall mechanism is illustrated in equation 129. 

Whereas conversion of sulfoxides to the corresponding a-acyloxysulfides by acid anhydrides, for example acetic anhydride, the Pummerer reaction [1], has been known for quite a time, the conversion of sulfoxides with silylating reagents via the unstable intermediate O-silyl compounds to a-silyloxysulfides, the Sila-Pummerer reaction is a relatively new reaction, which has recently been reviewed [1—4-]. 

The differing nucleophilicity of acetate and trifluoroacetate anion determined the manner in which naphtho[l,8-/yt]-l,5-dithiocinc sulfoxide 127 rearranged on treatment with acetic and trifluoroacetic anhydrides. In both cases, the reaction proceeded through formation of a disulfonium dication 128, but the final products were different. When acetic anhydride was used, the reaction afforded the corresponding a-acetylsulfide 130, a normal product of the Pummerer rearrangement, while trifluoroacetic anhydride caused isomerization with formation of dithioacetal 132 (see Scheme 16) <1995HAC559>. 

Pummerer-type dehydration of the sulfoxide 408 using acetic anhydride results in efficient formation of the 1,3-dipolar compound 409 which is able to undergo cycloaddition with dienophiles to generate tricyclic compounds such as 410 in good yield (Scheme 31) <2000T10011>. 

Monosulfoxide 13 undergoes the Pummerer rearrangement when treated with acetic anhydride in the presence of sodium acetate.85 The experiments with tetradeuterated and 180-labeled sulfoxide confirm intermediate formation of a dication.86 The ratio of 2,8,8-trideuteriated to 4,4,6,6-tetradeuteriated product 37 is equal to the intramolecular isotope effect ku k0 =1.7 (Scheme 21).85... 

On treatment with dimethyl sulfoxide-acetic anhydride followed by sequential oximation, reduction, detritylation, and acid hydrolysis, a tetra-(6-0-trityl)-cyclohexaamylose was reported to afford 2-amino-2-deoxy-D-glucose, in addition to D-glucose, indicating459 that... 

Useful syntheses of D- and L-lyxose from 1,3-O-benzylidene-D- and L-arabinitol have been achieved through the highly selective oxidation of the primary hydroxyl groups by dimethyl sulfoxide-dicyclohexylcarbodiimide.463 Oxidation of but one of the two (equivalent) hydroxyl groups in 1,3,4,6-tetra-O-benzyl-D-mannitol464 and l,6-di-0-benzyl-2,5-0-methylene-D-mannitol465 was possible with dimethyl sulfoxide-acetic anhydride. 

The acceleration of racemization of sulfoxides in acetic anhydride by adding Lewis acids, such as AICI3 (271,276,277), is consistent with the mechanism above, since the formation of acetoxysulfonium ion is facilitated. 

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