Within the framework of investigations of the rearrangement-cyclization reaction, discovered recently by us, of chloroethoxy-sym-triazines into annelated sym-triazinones [1] it was found that on thermolysis 4-alkyl-2-(2-chloroethoxy)-6-dialkylamino-sym-triazines split off hydrogen chloride or are subject to dechloroalkylation with the formation of 8-alkyl-4,6,7,8-tetrahydroimidazo[1,2-a]-1,3,5-triazin-4-ones [2]. The high phyto and fungal activity of oxazole derivatives [3-5] directed the search for new pesticides towards the series of 8-substituted derivatives of imidazo-sym-triazinones. Using the basic approaches of the indicated procedure the corresponding chloroethoxy derivative 2 was obtained from the quaternary ammonium salt 1. On thermolysis and subsequent alkaline treatment compound 2 is converted into the methyl ester of (2-dimethylamino-4-oxo-6,7-dihydro-4H-imidazo[1,2-a]-1,3,5-triazin-8-yl)acetic acid (3) and then into the corresponding hydrazide 4 (Table 1). In place of the triplet signals of the chloroethoxy group of compound 2 a multiplet is observed characteristic of the methylene groups of the imidazole ring of compounds 3 and 4 (Table 2).In addition, a simpler and more effective procedure for the synthesis of a series of 8-alkyl-substituted imidazo-sym-triazinones was, in our opinion, the use of 2-substituted 7,8-dihydro-6H-imidazo[1,2-a]-1,3,5-triazin-4-one as starting material. As an example, 2-dimethylamino-7,8-dihydro-6H-imidazo[1,2-a]-sym-triazin-4-one 5 was synthesized by a similar cyclization procedure from 6-chloroethylamino-4-dimethylamino-2-methoxy-sym-triazine [6]. It was shown that compound 3 is also formed on alkylation of compound 5 with methyl bromoacetate in DMF and in the presence of potassium hydroxide (Tables 1, 2).Urea derivatives 6a-d were formed on boiling a toluene solution of compound 5 with aryl isocyanates. N-Acetyl (7) and N-arenesulfonyl (8a-c) derivatives were obtained by acetylation and arenesulfonylation of compound 5. _______