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A convenient synthesis of new 2-phenylthieno[3,2-e][1,2,4]triazolo[1,5-c] pyrimidine derivatives by dimroth rearrangement
Son, Hoon Young,Song, Yang-Heon
experimental part, p. 350 - 353 (2010/08/22)
A series of thienotriazolopyrimidine compounds 4 were designed and synthesized. The compounds 4 were prepared through a series of reactions starting with 2-aminothiophene-3-carbonitrile. The hydrazone derivatives were synthesized by condensation of hydrazine compounds with the corresponding benzaldehydes in toluene in the presence of catalytic amount of p-toluene sulfonic acid. When each of 4 was heated in ethanol in the presence of odium acetate, they isomerized to the thermodynamically more stable compounds 5 through successive ring opening and ring closing by Dimroth-type rearrangement. In order to provide a decisive evidence for the exact structure of 5, the product 5a was compared with authentic sample prepared by alternative syntheses. The most prominent peak of 4a was observed at 9.02 as a singlet attributed to the pyrimidine proton, whereas the similar singlet of 5a was observed at 9.27 in more down field.