Efficient Synthesis of Benzothieno[3,2-d]-1,2,4-triazolo [1,5-a]pyrimidin-5(1H)-ones via a Tandem aza-Wittig/Heterocumulene-Mediated Annulation

摘要

The carbodiimides 2, obtained from reactions of iminophosphorane 1 with isocyanates, reacted with hydrazine to give selectively 3-amino-2-arylaminobenzothieno[3,2-d]pyrimidin-4(3H)-ones 4. Reactions of 4 with triphenylphosphine, hexachloroethane, and Et3N produced iminophosphoranes 5. A tandem aza-Wittig reaction of iminophosphorane 5 with isocyanate, acyl chloride generated benzothieno[3,2-d]-1,2,4-triazolo[1,5-a]pyrimidin-5(1H)-ones 7 and 9 in satisfactory yields. The effects of the nucleophiles on cyclization have been investigated.