A new synthesis of 2,8-disubstituted pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines

A practical synthesis of pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines, which are key intermediates in the preparation of adenosine receptor antagonists, is developed. The method allows introduction of a variety of aryl substituents at position 2 of the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine system via cyclocondensation of 5-amino-4-iminopyrazolo[3,4-d]pyrimidine with benzaldehydes accompanied with oxidation by iodobenzene diacetate. Some unexpected reactions are observed and the structures of the products are confirmed using NMR spectroscopy and X-ray crystallography. (C) 2009 Elsevier Ltd. All rights reserved.