The o. formylarylazomethylenetriphenylphosphora... carrying an electron withdrawing group on the ylidic carbon undergo thermal intra molecular cyclization to 3-oxo-indazolin-2-yl- methylenetriphenylphosphorane derivatives. The latter compounds, and their 1-alkyl derivatives, in turn, undergo thermal and/or acid catalyzed rearrangement to 4-oxo-l, 4- dihydroquinazoline derivatives and PPh3. Some possible reaction mechanisms are ...
