Phosphoramidates as Transient Precursors of Nitrogen-Centered Radical Under Visible-Light Irradiation: Application to the Synthesis of Phthalazine Derivatives

Phosphoramidates are for the first time presented as efficient N-Centered Radical (NCR) precursors under visible-light irradiation. More precisely among this class of phosphorus-derived compounds, we studied the radical reactivity of phosphonohydrazones, under mild reaction conditions, which allowed the synthesis of a wide and diversified library of the scarcely reported phthalazine scaffold. Mechanistic investigations confirmed the formation of a NCR from these brand-new phosphonohydrazones (derivatived from phosphoramidates), which were further engaged in an intramolecular 6-exo-dig cyclization to provide phthalazines. Compared to other pre-activated moieties, the phosphoramidate group is self-immolative, thus enhancing its attractiveness for the C-N bond formation.