THERMAL-ISOMERIZATION OF 2-ACYLOXY-4,6-DIMETHOXY-1,3,5-TRIAZINES TO 3,5-DIMETHYL-1,3,5-TRIAZIN-2,4,6(1H,3H,5H)-TRIONES - CRYSTAL-STRUCTURE OF -3,5-DIMETHYL-1,3,5-TRIAZIN-2,4,6(1H,3H,5H)-TRIONE

2-(2,2-Dimethylpropanoyloxy)-4,6-dimethoxy and 2-(benzoyloxy)-4,6-dime thoxy-1,3,5-triazine underwent thermal isomerization affording in almo st quantitative yield isocyanuric acid derivatives: -3,5-dimethyl-1,3, 5-triazin-2,4,6(1H,3H,5H)-trione and 1-benzoyl analog, respectively. T he stepwise mechanism involving O --> N acyl and methyl group migratio ns was studied by means of H-1-NMR. The structure of 2,2-dimethylpropa noyl derivative was confirmed by X-ray method. Exocyclic carbonyl grou p in this crystal structure is perpendicular to ring plane excluding c onjugation of N lone pair electrons with carbonyl pi system. Thus exoc yclic N-C(O) bond distance equals 1.483(5) Angstrom as compared with 1 .35 to 1.38 Angstrom found for endocyclic N-C distances in the same st ructure.