Flash vacuum pyrolysis of azolyl-malonamates. Synthesis of 5-hydroxy-azolopyrimidin-7-ones

Abstract

The synthesis and flash vacuum pyrolysis (fvp) reactions of ethyl 3-oxo-3-(1,3-thiazol-2ylamino)propanoate (1) and of ethyl 3-oxo-3-(4H-1,2,4-triazol-3-ylamino)propanoate (2) are described in this article. The synthesis of both compounds was performed by reaction of the corresponding aminoheterocycle and diethylmalonate with higher yields than previously described methodologies. Flash vacuum pyrolysis reactions of 1 were performed between 300 and 500oC. Reactions between 300 and 430oC afforded ethanol and 5-hydroxy-7H-[1,3]thiazolo[3,2-a]pyrimidin-7-one (3) and between 450 and 500oC carbon suboxide (4), 2-aminothiazole (5) along with 3 and ethanol were formed. Compounds 4 and 5 were formed a higher temperatures from 3, as was demonstrated by an independent reaction of 3. Reactions of 1 over solid catalysts (zeolites and hydrotalcites) were also carried out. In both cases they afforded about 40% of 3 at 250oC. Flash vacuum pyrolysis reactions of 2 were carried out between 300 and 450oC. Up to 430oC the isolated products were ethyl-3-(3-amino-1H-1,2,4-triazol-1-yl)-3-oxopropanoate (6), 5hydroxy[1,2,4]triazolo[1,5-a]pyrimidin-7(4H)-one (7) and ethanol. From 430 to 450oC decomposition of 2 by a different mechanism than reactions at lower temperatures afforded 1,2,4-triazole (8), ethoxyoxazirene (9) and probably ketene (10) (not detected). Reaction paths explaining reactions of 1 and 2 are discussed.