RACEMIC 1-METHYL-1,2,4-TRIAZOLIDINE-3,5-DIONE (1-METHYLURAZOLE) - DEFINITIVE CHARACTERIZATION OF PYRAMIDAL HYDRAZIDE N-ATOMS AND RACEMATE INTERMOLECULAR HYDROGEN-BONDING

In contrast to the rapid formation of ribosides of urazole and 4-methylurazole through a hydrazide N atom, 1-methylurazole, C3H5N3O2 (I), fails to exhibit any reactivity with ribose; this has been evaluated crystallographically. The X-ray structure of (I) shows the imide N atom to be trigonal but both hydrazide N atoms to be pyramidal, with N1-C6 and N2-H trans, affording a torsion angle C6-N1-N2-H2 of -49(2)degrees. These data suggest that attack on the N2 electron lobe of (I) must be cis to the N1 methyl, invoking a sterically hindered, relatively high-energy transition state and intermediate. The crystal structure shows both enantiomers, 1R,2R and 1S,2S, in a three-dimensional network of intermolecular N-H...O=C hydrogen bonds.