Structure and Conformations of Monoacyl and Diacyl 1,2,4-Triazolidine-3,5-diones

A series of monoacyl and diacyl 1,2,4-triazolidine-3,5-diones substituted at position 4 with either a phenyl or a tert-butyl group was prepared. Both acetyl and benzoyl groups were utilized as the acyl substituents. The diacylated compounds containing one or two acetyl groups were somewhat unstable to moisture. The acylated compounds were studied by (1)H, (13)C and (15)N NMR spectroscopy and X-ray crystallography to determine if they were acylated on nitrogen or ring carbonyl oxygen. The results indicated that the acylations occurred on nitrogen. The NMR spectra and molecular modeling computations were used to assign conformations to several of the diacylated compounds.