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.

Several N-methylenefluoroacetamides were synthesised and tested for contact (2 days) and systemic (7 days) activity against APhis fabae. The contact activity seemed to depend on the ease of hydrolysis to fluoroacetamide. Generally, the systemic activity of the compounds was similar to that of fluoroacetamide, indicating that, during the longer period allowed for the systemic tests, hydrolysis to fluoroacetamide took place as the first step. Some compounds were too stable and showed little contact or systemic activity. The acaricidal activity and mammalian toxicity were also determined. A hydrolysis path is indicated, and the greater stability of certain derivatives is discussed.