Phosphorous pentoxide, DMSO

A protocol has been reported based on a cyclization procedure followed by hydrolysis and oxidation, which allowed the preparation of a-keto-(3-lactams (Scheme 11), [59]. The cyclization of imines with acetylglyoxylic acid, in the presence of POCI3 and Et3N, gave 3-acetoxy-(3-lactams in good yields as cis-isomers, prevalently. These latter were hydrolyzed to alcohols in excellent yields under very mild conditions. Subsequent oxidations were performed by treatment with dimethyl sulfoxide (DMSO) in the presence of phosphorous pentoxide to give a-keto-(3-lactams. More 2-azetidinones were synthesized varying the substituent of the acetyl moiety. 

Despite this they should be considered as possible alternatives in cases where more familiar methods fail. Amongst this group of activators are p-toluenesulfonyl chloride, tiifluoromethanesulfonic anhy-dride,silver tetrafluoroborate, molybdenum oxide, phosphorous pentoxide, trichloromethyl chloroformate, 2-fluoro-l-methylpyridiniumsulfonate, chlorosulfonyl isocyanate, antimony penta-chloride (for which an X-ray structure of the DMSO-SbCb conqilex was obtained) and phenyl dichlo-rophosphate. ... 

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