Dicyclohexylcarbodiimide, DMSO activator

There are several methods reported in the literature for transforming vicinal diols into ct-diketones while avoiding the risk of C-C bond cleavage.26 Examples include the standard Swem conditions (dimethyl sulfoxide and oxalyl chloride followed by triethylamine), or the use of DMSO activated by acetic anhydride, pyridine-sulfur trioxide complex, or dicyclohexylcarbodiimide (Mq/J-att oxidation). Diones are also obtained by treatment with benzalacetone as a hydride acceptor in the presence of catalytic amounts of tris(triphenylphosphine)ruthenium dichlonde [(PPh RuCFl.27 Recent developments include the use of w-iodoxyben/.oic acid28 or the oxoammonium salt of 4-acctamidoletramethylpipcridine-1-oxyl and y -toluencNulfonic acid.29... 

The Pfitzner-Moffatt oxidation utilises 1,3-dicyclohexylcarbodiimide as the DMSO activator in the presence of acid to afford oxidation of alcohols to carbonyls.2,24,25 Initial work was carried out on steroids and thymidine residues although the procedure has since been found to be applicable to a large range of alcohols. In the following example, the Pfitzner-Moffatt method was used as an alternative to the Swem reaction which had resulted in the formation of an unwanted a-chloroketone (see later).26 Other oxidation procedures were attempted (PDC, PCC, Dess-Martin periodinane) however the Pfitzner-Moffatt gave the best, albeit modest, yield. 

Note Pfitzner-Moffatt reaction represents oxidation of primaiy and secondary alcohols by dimethyl sulfoxide (DMSO) activated with carbodiimides, usually dicyclohexylcarbodiimide (DCC). Intermediary alkoxysulfonium ylides rearrange to aldehydes or ketones. This reaction yields urea as a by-product that is difficult to... 

The most intensively studied oxidizing system is that developed by Pfitzner and Moflatt in which the oxidation is carried out at room temperature in the presence of dicyclohexylcarbodiimide (DCC) and a weak acid such as pyridinium trifluoroacetate or phosphoric acid. The DCC activates the DMSO which in turn reacts with the carbinol to give an oxysulfonium intermediate. This breaks down under mild base catalysis to give the desired ketone and dimethyl sulfide. 

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