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

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(3H)-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(3H)-ones 7 or 9, respectively, in satisfactory yield. The aza-Wittig reaction of iminophosphorane 5 with CS2 or CO2 gives the 1,2,4-triazolo[5,1-b]quinazolin-9(3H)-ones 14 or 17, respectively. Further S-alkylation of 14 produces the 2-alkylthio-1,2,4-triazolo[5,1-b]quinazolin-9(3H)-one 15. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)