Ruthenium(II)-catalyzed C–H activation/C–N bond formation via in situ generated iminophosphorane as the directing group: construction of annulated pyridin-2(1H)-ones

We describe an efficient and straightforward synthesis of annulated pyridin-2(1H)-ones following condensation of acyl azides with internal alkynes via the ruthenium-catalyzed ortho C–H bond activation. The reaction in DCE proceeds via in situ generation of iminophosphoranes as directing group-coordination of Ru with N-atom-ortho cyclometallation-insertion of an alkyne into the Ru–C bond-protonation-reductive elimination in a domino sequence. The role and stability of in situ generated iminophosphorane and ruling out the possibility for the benzamide involvement was established using 1H and 31P NMR experiments.