Cyclocondensation reactions of 3-amino-2-hydrazino-4(3H)-pyrimidinones. Formation of 1,2,4-triazolo[4,3-a]pyrimidines and pyrimido[1,2-b][1,2,4,5]tetrazines

A new one‐step synthesis of pyrimido‐[1,2‐ b ][1,2,4,5]tetrazines

“…1 H NMR spectra were recorded on a Varian Gemini 200 spectrometer in deuterated chloroform with use of tetramethylsilane (TMS) as an internal reference. IR spectra were determined with a Fourier Transform and Pye Unicam Infrared spectrophotometer using a KBr wafer.…”

“…So far, only one method has been reported in the literature for the synthesis of the pyrimido [1,2-b] [1,2,4,5]tetrazine ring system [1]. Such a method involves the reaction of 3-amino-2-hydrazino-4(3H)-pyrimidinones 1 with ortho esters, dimethylformamide dimethyl acetal, or diethoxymethyl acetate in glacial acetic acid at room temperature [1].…”

“…Such a method involves the reaction of 3-amino-2-hydrazino-4(3H)-pyrimidinones 1 with ortho esters, dimethylformamide dimethyl acetal, or diethoxymethyl acetate in glacial acetic acid at room temperature [1]. Such reactions were reported, however, to yield a mixture of pyrimido [1,2- [4,3-a]pyrimidines 3, and the yields of the former were in the range of 15-51% (Equation 1) [1]. Our continued interest in the chemistry of hydrazonoyl halides 4 [2] prompted us to investigate their reactions with N-aminoheterocyclic thiols in an attempt to develop a new strategy for synthesis of the title ring system.…”

“…The interest in developing new simple syntheses of pyrimido [1,2- megalovirus protease [3]. Here, we wish to report our results utilizing reactions of 4 with 3-amino-2,3-dihydro-6-methyl-2-thioxo-4(1H)-pyrimidinone 5 and 3-amino-6-methyl-2-methylthio-4(3H)-pyrimidinone 6 as a route to 6H-pyrimido [1,2,-b] [1,2,4,5]tetrazin-6-ones 9 (Scheme 1). The latter can now be readily prepared with a variety of substituents and in good overall yields (see Experimental section).…”

“…The same results were obtained when the reactions of 4 with 5 were carried out in pyridine at reflux. It was initially anticipated that such reactions would yield the respective pyrimido [2,1-b] [1,3,4]thiadiazines by analogy to the reactions of 4 with 2-aminothiophenol, which were reported to afford benzothiadiazine derivatives [4]. Unexpectedly, the products isolated from the reactions of 5 with 4a-h were found to be free of sulfur.…”