ul. Zorge, 344090 Rostov on Don, Russian Federation Recyclization of thieno[3,2 e][1,2,4]triazolo [4,3 c]pyrimidines was studied experimen tally and theoretically by B3LYP/6 31G** calculations in the gas phase and in solution (EtOH). The experimentally observed characteristic features of the isomerization (the possibility of the Dimroth rearrangement occurring by the ANRORC mechanism and high energy barriers in acid catalyzed reactions) were confirmed by quantum chemical calculations. Substituents in the triazole ring were found to play the principal role in the rearrangement.

7H Pyrrolo[3,2 e] [1,2,4]triazolo [1,5 c]pyrimidines were synthesized by the reactions of 2 ethoxymethyleneamino 1H pyrrole 3 carbonitriles with acid hydrazides and by the reac tions of aminoiminopyrimidines (prepared based on the above mentioned carbonitriles) with acid chlorides.

Formimidic acid esters derived from 1-substituted 5-aminopyrazole-4-carbonitriles reacted with carboxylic acid hydrazides on heating to give 2,7-disubstituted pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives as a result of double heterocyclization. The same compounds were obtained by thermal recyclization of 1-aroyl-2-(1-R-pyrazolo[3,4-d]pyrimidin-4-yl)hydrazines.

Fused pyrimidine derivatives R 0515 Synthesis and Rearrangements of 7H-Pyrrolo[3,2-e][1,2,4]triazolo[1,5-c]-and 7H-Pyrrolo[3,2-e][1,2,4]triazolo[4,3-c]pyrimidines. -New preparative routes for the synthesis of triazolo[1,5-c]pyrimidines, much simpler than the widely used methods, are developed. -(VOROB'EV, E. V.; KURBATOV, E. S.; KRASNIKOV, V. V.; MEZHERITSKII*, V. V.; USOVA, E. V.; Russ.

Fused pyrimidine derivatives R 0515 Alternative Routes to the Pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine System. -Various kinds of compounds such as (I) are synthesized. -(TYURIN, R. V.; VOROB'EV, E. V.; MINYAEVA, L. G.; KRASNIKOV, V. V.; MEZHERITSKII, V. V.; Russ. J. Org. Chem. 41 (2005) 6, 916-921; Inst. Phys. Org. Chem., Rostov State Univ., Rostov-on-Don 344090, Russia; Eng.) -K. Schneider 05-154