New Efficient Synthesis of 1,2,4‐Triazolo[5,1‐b]quinazolin‐9(3H)‐ones via a Tandem Aza‐Wittig/Heterocumulene‐Mediated Annulation

Abstract

Abstract The carbodiimides 2 , obtained from aza‐Wittig reactions of iminophosphorane 1 with aromatic isocyanates, react with hydrazine to give, selectively, the 3‐amino‐2‐arylaminoquinazolin‐4(3 H )‐ones 4 . Reaction of 4 with triphenylphosphane, hexachloroethane and triethylamine produces iminophosphoranes 5 . A tandem aza‐Wittig reaction of iminophosphorane 5 with isocyanate or acyl chloride generates the 1,2,4‐triazolo[5,1‐ b ]quinazolin‐9(3 H )‐ones 7 or 9 , respectively, in satisfactory yield. The aza‐Wittig reaction of iminophosphorane 5 with CS 2 or CO 2 gives the 1,2,4‐triazolo[5,1‐ b ]quinazolin‐9(3 H )‐ones 14 or 17 , respectively. Further S‐alkylation of 14 produces the 2‐alkylthio‐1,2,4‐triazolo[5,1‐ b ]quinazolin‐9(3 H )‐one 15 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)