The Dimroth rearrangement: Synthesis and interconversion of isomeric triazolothienopyrimidines

Article abstract of DOI:10.3184/030823408X327875

Triazolo-thieno[3,2-e]pyrimidines obtained by cyclisation of 4-hydrazino-2-(methylthio)thieno[2,3-d]pyrimidine with formic acid, acetic acid, cyanogen bromide and carbon disulfide, and by oxidation of the derived aldehyde hydrazones, are found to be the triazolo[4,3-c] isomers. These [4,3-c] compounds resist isomerisation in acid, but they undergo Dimroth rearrangement to the [1,5-c] isomers under basic conditions. The crystal structure of one such rearranged product, 5-methoxy-8,9,10,11-tetrahydro[1]benzothieno[3,2-e][1,2,4] triazolo[1,5-c]pyrimidine (13b) was confirmed by X-ray analysis.