Synthese von 2‐Methyl‐4H‐1,3‐benzoxazin‐4‐onen und analogen Verbindungen

Synthesis of 2‐Methyl‐4H‐1,3‐benzoxazin‐4‐ones and Related Compounds 4H‐1,3‐benzoxazin‐4‐ones 2 are smoothly prepared via (acylimino)phosphoranes 1 by intramolecular condensation analogous to a Wittig reaction. Tert. phosphanes are used for the preparation of the (acylimino)phosphoranes 1 which are converted into the corresponding benzoxazines and tert. phosphane oxides, e.g. 2‐methyl‐4H‐1,3‐benzoxazin‐4‐one (2a) which, in spite of some attempts, has not been obtained before.