Reaction of β-Keto Esters with 2-Amino-1,3,4-thiadiazoles. A Reinvestigation

Article abstract of DOI:10.1021/jo01312a012

2-Amino-5-substituted-1,3,4-thiadiazoles react with ethyl acetoacetate under basic conditions to give 3-oxo-N-(5-substituted-1,3,4-thiadiazol-2-yl)butanamides 4.During acid cyclization, 4 rearranges to give a mixture of thiadiazolopyrimidones 3 and 5, the ratio varying with the nature of the substituents.Under acidic conditions, the butenoic ester 2 can also be isolated; however, it does not rearrange and yields only the expected 3.With ethyl benzoylacetate under acidic and basic conditions, only one compound is formed whose structure was determined as the enol form of 4d by X-ray diffraction.In strong acid, it also cyclizes and rearranges to give a mixture of 3 and 5 in a 9:1 ratio.