Fluorous extraction, Swern oxidation

Fluorous-tagged reagents are very attractive for reactions in which a stoichiometric by-product is formed that is difficult to separate. An example is perfluor-oalkylated triphenylphosphane for use in Wittig and aza-Wittig reactions, where the corresponding phosphane oxide is removed by fluorous extraction [22, 23]. Similarly, fluorous sulfoxide has been employed in Swern oxidations, and fluorous carbodiimide has been used as a coupling reagent [24, 25]. 

Experimental Protocol. The experimental protocol for using fluorous sulfoxide 1 in the Swern oxidation is similar to the original one where DMSO is used except for the work-up details. The reactions are typically run in anhydrous CH2CI2 at —30°C for 1-2 h and then warmed to room temperature for 1 h. The reaction mixture is diluted with H2O, washed with saturated NH4CI solution, and then extracted with CH2 CI2. CH2 CI2 is subsequently... 

A fluorous analogue of DMSO has been used to perform Swern reactions [24], This widely used method of oxidizing an alcohol to an aldehyde falls down seriously from the environmental point of view due to its production of a stoichiometric amount of dimethyl sulfide. Here, a fluorous sulfoxide is prepared and used in the oxidation of several alcohols in dichloromethane, as shown in Scheme 9.12. After reaction, the sulfide is extracted into perfluorohexane and the system recycled. Unfortunately, extraction from dichloromethane was found to be difficult, but replacing the dichloromethane with toluene leads to a more efficient recovery. 

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