Synthesis of 2-substituted oxazoloquinazolinones

The reaction of methyl 2-isothiocyanatobenzoate and 1-azido-3-(4-substituted phenyl)propan-2-ones in the presence of triphenyl phosphine in dioxane by heating produced tricyclic ( Z )-2-(4-substituted benzylidene)-2,3-dihydro-5 H -oxazolo[2,3- b ]quinazolin-5-ones instead of the expected methyl 2-{[5-(4-substituted benzyl)oxazol-2-yl]amino}benzoates. A one-pot procedure for the synthesis of 2-substituted 5 H -oxazolo[2,3- b ]quinazolin-5-ones from appropriate azidomethyl ketones and 2-isothiocyanatobenzoate was developed.