Substituted oxazolid-2,4-diones have been prepared from N-substituted carbarnates and a-chloroacyl chlorides. The intermediate N-substituted chloroacylcarbamates cyclise at higher temperatures t o t h e diones. The plots of t h e cyclisation rates of ethyl N-alkyl-N-chloroacetylcarbamates were straight, and steric effects influenced the cyclisation. Infrared spectra of t h e N-substituted chloroacylcarbamates and of 3-substituted oxazolid-2,4-diones are discussed.%SUBSTITUTED oxazolid-2,4-diones (111) are an important class, as several members possess analgesic and anti-epileptic properties. 3-Alkyl derivatives have been prepared by alkylation of oxazolid-2,4-dione 193-5 or by treatment of a-hydroxy-esters with alkyl isocyanates and cyclisation of the resulting urethanes, by which method also the 3-aryl derivatives have been synthesised. 6 We found that a convenient preparation of 3-alkyl-and 3-aryl-oxazolid-2,4-diones was to heat at >180" lower alkyl alkyl-or aryl-carbarnates (I) with an a-chloroacyl chloride, according to the scheme shown.

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