Isolation, Reactivity and Intramolecular Trapping of Phosphazide Intermediates in the Staudinger Reaction of Tertiary Phosphines with Azides

The Staudinger reaction of the N-substituted o-azidobenzamide 1 with triphenylphosphine or diphenylmethylphosphine allows the isolation of the intermediate phosphazides as crystalline solids, which have been characterized by spectroscopic methods. These compounds react in aza Wittig type fashion with isocyanates to give unexpectedly the corresponding 1,2,3-benzotriazinone derivative. Trapping of a Z-phosphazide by intramolecular aza Wittig reaction is reported for the first time.