Trifluoroacetic anhydride-activated DMSO

The use of trifluoroacetic anhydride for the activation of DMSO in the oxidation of alcohols was first attempted by Albright and Goldman in 196 5.119,120 According to these authors, who tried the reaction at room temperature, trifluoroacetic anhydride is not effective in the activation of DMSO. Later, Swern et al. made a detailed study of the interaction of DMSO with TFAA,121 and proved that the resulting activated DMSO is stable at low temperature and can be used in the oxidation of alcohols. In... 

Interestingly, although trifluoroacetic anhydride reacts very quickly with alcohols, the reaction with DMSO is even quicker. Therefore, the formation of the activated DMSO species 22 can be made in the presence of the alcohol, resulting in little erosion of the oxidation yield. 

The activation of DMSO by electrophilic reagents such as oxallyl chloride or trifluoroacetic anhydride (TFAA) (among many others) produces an oxidant capable of oxidizing primary alcohols to aldehydes in high yields. This oxidation is called the Swern oxidation and yields the aldehyde (oxidized product) by reductive elimination of dimethylsulfide (reduced product) and proceeds under mild, slightly basic conditions. It is a second widely used and effective oxidative method for the production of aldehydes from primary alcohols. 

The presence of amino substituents in the 2- or 5-position activates the oxazole ring (4-aminooxazoles are unknown). Thus 2-amino-3-aryloxazoles yield the derivatives (127 X = Cl or Br) on halogenation, and nitration of 2-dimethylamino-4-phenyloxazole afforded 2-dimethylamino-5-nitro-4-(4-nitrophenyl)oxazole, the sole example of direct nitration of the oxazole ring. 5-Dialkylamino-2-phenyloxazoles react with trifluoroacetic anhydride to form the ketones (128) and they couple with arene diazonium fluoroborates the products (129) readily rearrange to 1,2,4-triazoles (130) in DMSO solution. 

Trifluoroacetic anhydride (TFAA) is also a very potent activator for DMSO and concomitant trifluoroacetylation of the starting alcohol is usually not observed [27]. Both the Swem and the TFAA procedure are carried out at low temperature to prevent undesired side reactions, particularly formation of the methylthiomethyl ether. Before these two methods became developed, acetic anhydride was often used for DMSO activation. Flowever, the oxidation under these conditions is slower and the methylthiomethyl ether byproduct is often observed [27]. 

Derived reagents. Mancuso and Swern2 have reviewed activated dimethyl sulfoxide reagents (100 references). Activation of DMSO with either trifluoroacetic anhydride (7, 136) or oxalyl chloride (8, 200) provides the most generally useful... 

Cr is also advantageous from an environmental point of view. Various methods for the activation of DMSO have been developed, and activation with trifluoroacetic anhydride (TFAA) is frequently employed in modern organic synthesis. It is well known that a reactive species generated by the... 

C.i. Swern Oxidation. The variation that is probably the most common in synthesis was discovered by Swern, who found that DMSO can be activated for the oxidation of alcohols by addition of trifluoroacetic anhydride. 6 The reaction is usually done in dichloromethane at temperatures below -30°C. The initially... 

The solvent effect in Mn2(CO)io polymerizations was explored with over 40 solvents [51] and perfluorobutyl iodide (PFBI), easily activated by Mn(CO)5 (vide infra) was used as initiator. The comparisons were made under the same conditions (VDF/PFBI/Mn2(CO)io = 25/1/0.2 VDF/solvent = 1/3 wt/v) and revealed that in accordance with the principles outlined above, no polymerization occurred in anisole, a,a,a-trifluorotoluene, diglyme, diethylene glycol monoethyl ether, ethyl ether, THF, dioxane, o-cresol, isopropanol, trifluoroacetic anhydride, tetramethylurea, sulfolane, benzonitrile, cyclopentanone even after 1-3 days. Poor reaction rates (/ p PP < 1 - 9 X 10 h ) were observed in HMPA, 2-butanone, methyl pentanone, DMF, DMSO, PEO, DMAc, 5-valerolactone, BuOH, and EtOAc. Slightly faster polymerizations (/ p PP = 1 - 1.7 X 10 h ) were seen in CH2CI2, acetic anhydride, y-butyrolactone, 1,2-dichloroethane, TMP, MeOH, pentafluorobutane, and HFBz,... 

Oxidative Methods.— The oxidation of alcohols to carbonyl compounds using DMSO activated by electrophiles, e.g. oxalyl chloride or trifluoroacetic anhydride, has been reviewed/ DMSO-Metal oxide oxidations of alcohols have been described using molar, or catalytic, amounts of a new oxide of molybdenum/ This yellow oxide, Mo-y , is prepared by hydrogen peroxide oxidation of molybdenum or its trioxide/ N Iodosuccinimide in combination with tetra-butylammonium iodide oxidizes primary and secondary alcohols to aldehydes and ketones in dichloromethane solution/ The corresponding bromo-combina-tion gave inferior yields, and the chloro-combination resulted in polychlorination of the carbonyl product. 

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