Oxidations sulfur trioxide-pyridine

The use of dimethyl sulfoxide-acetic anhydride as a reagent for the oxidation of unhindered steroidal alcohols does not appear to be as promising due to extensive formation of by-products. However, the reagent is sufficiently reactive to oxidize the hindered 11 j -hydroxyl group to the 11-ketone in moderate yield. The use of sulfur trioxide-pyridine complex in dimethyl sulfoxide has also been reported. The results parallel those using DCC-DMSO but reaction times are much shorter and the work-up is more facile since the separation of dicyclohexylurea is not necessary. Allylic alcohols can be oxidized by this procedure without significant side reactions. 

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)... 

Methacycline Methacycline, 4-dimethylamino-l,4,4a,5,5a,6,ll,12a-octahydro-3,6,10, 12,12a-pentahydroxy-6-methylen-l,ll-dioxo-2-naphthacencarboxamide (32.3.6), is synthesized from oxytetracycline (32.3.2), which is reacted with a sulfur trioxide— pyridine complex, resulting in an oxidation reaction. Simultaneous sulfonation gives a naphthacen-snlfotetrahydrofuran derivative intermediate (32.3.5), which when reacted with hydrofluoric acid forms methacycline (32.3.6) [222-225]. 

By a suitable choice of activating reagents, primary and secondary alcohols can be selectively oxidized to carbonyl compounds in good yields at room temperatures. Typical activating reagents ate acetic anhydride, sulfur trioxide—pyridine, dicyclohexyl catbodiimide, and phosphorus pentoxide (40). 

Furan is resinified by sulfuric acid but it can be sulfonated with the complex of sulfur trioxide with pyridine or dioxane. Depending on conditions the 2-sulfonic or the 2,5-disulfonic acid may be obtained. Furan-2-carboxylic acid can be sulfonated with oleum. Benzo[6]furan is polymerized by sulfuric acid. The 2-sulfonic acid has been obtained by oxidation of the sulfinic acid available in turn by treatment of the lithio derivative with sulfur dioxide. Benzo[6]furan with the sulfur trioxide-pyridine complex allegedly affords the 3-sulfonic acid. 

Silyl ethers of aliphatic alcohols are inert towards strong bases, oxidants (ozone [81], Dess-Martin periodinane [605], iodonium salts [610,611], sulfur trioxide-pyridine complex [398]), and weak acids (e.g., 1 mol/L HC02H in DCM [605]), but can be selectively cleaved by treatment with HF in pyridine or with TBAF (Table 3.32). Phenols can also be linked to insoluble supports as silyl ethers, but these are less stable than alkyl silyl ethers and can even be cleaved by treatment with acyl halides under basic reaction conditions [595], Silyl ether attachment has been successfully used for the solid-phase synthesis of oligosaccharides [600,601,612,613] and peptides [614]. 

The above discussion has concentrated upon the reagents used, but it is equally of value to comment on the substrate, particularly in reactions for which other oxidation methods have been reported to fail. A good example is the oxidation of the iron-carbonyl complex (31) to the ketone (32 equation 14). The use of dimethyl sulfoxide activated with sulfur trioxide-pyridine complex gave a 70% yield of the product, in contrast to the use of the Pfitzner-Moffatt procedure (dimethyl sulfoxide-DCC) or the chromium... 

One of the best activators for dimethyl sulfoxide is the complex of sulfur trioxide/pyridine, which in the presence of triethylamine rapidly oxidizes primary and secondary alcohols to aldehydes and ketones in very good yields at ambient temperature. This reagent also allows the very use l conversion of allylic alcohols to the conesponding a,p-unsaturated carbonyl compounds. A further advantage of this procedure over many of the others is the ease of work-up, especially over the dimethyl sulfoxide-dicy-clohexylcarbodiimide method. 

The sulfur trioxide-pyridine activated dimethyl sulfoxide oxidation was also a key step in an excellent synthesis of the Pielog-Djerassi lactonic acid, being highly recommended as the test method to avoid epimerization of the C-2 center in the aldehyde (33). ... 

A second entry to dicarbonyl substrates utilizes the aldol reaction to establish the a-methyl center prior to oxidation of the p-hydroxyl moiety. Commonly, this oxidation is performed using the Sulfur Trioxide-Pyridine complex, which results in <1% epimerization of the methyl-bearing center (eq 34). Interestingly, this procedure procures the opposite methyl stereochemistry from that obtained through enolate acylation of the same enantiomer of oxazolidinone. 

Goh and Harvey effected the oxidation of the m-diol (3) to the o-quinone (4) efficiently by use of the sulfur trioxide-pyridine complex in DMSO-triethylamine. Use of DMSO-acetic anhydride (I, 305 2, 163-165 3,121-122) gave fair, but erratic yields of the quinones. Other reagents were completely unsuccessful. Note that oxidation... 

In the Pfitzner-Moffatt oxidation,4 an alcohol is oxidised by treatment with a mixture of dicydohexylcarbodiimide (DCC) (22), DMSO and an acid source, e.g. polyphosphoric acid, sulfur trioxide-pyridine, pyridine trifluoroacetate or acetic... 

Compound 22 was prepared by oxidation of P-amino alcohol 21 that was readily derived from Z-cysteine as shown in Fig (9). Although the oxidation of 21 by Swem oxidation proceeds in 81% yield, it requires cryogenic conditions as low as -bO C. In order to eliminate the impractical reaction conditions, an oxidation using sulfur trioxide pyridine complex (S03-py) [77] was examined (Table 1). Treatment of... 

The Collins/Sarett oxidation (chromium trioxide-pyridine complex), and Corey s PCC (pyridinium chlorochromate) and PDC (pyridinium dichromate) oxidations follow a similar pathway as the Jones oxidation (chromium trioxide and sulfuric acid in acetone). All these oxidants have a chromium (VI), normally black or yellow, which is reduced to Cr(IV), often green. 

Related Reagents. A/-Chlorosuccinimide-Dimethyl Sulfide Chromic Acid Dimethyl Sulfide-Chlorine Dimethyl Sulfoxide-Acetic Anhydride Dimethyl Sulfoxide-Dicyclo-hexylcarbodiimide Dimethyl Sulfoxide-Oxalyl Chloride Dimethyl Sulfoxide-Phosphorus Pentoxide Dimethyl Sulfoxide-Sulfur Trioxide/Pyridine Dimethyl Sulfoxide-Trifluoroacetic Anhydride Dimethyl Sulfoxide-Triphosgene Manganese Dioxide Pyridinium Chlorochromate Pyridinium Dichromate Ruthenium(rV) Oxide Silver(I) Carbonate on Celite 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3( 1 H)-ons. 

Sulfur trioxide-pyridine dimethyl sulfoxide Oxo compounds from alcohols Preferential oxidation... 

Iodine Acetaldehyde, acetylene, aluminum, ammonia (aqueous or anhydrous), antimony, bromine pentafluoride, carbides, cesium oxide, chlorine, ethanol, fluorine, formamide, lithium, magnesium, phosphorus, pyridine, silver azide, sulfur trioxide... 

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