Oxygen-Promoted 6- endo -trig Cyclization of β,γ-Unsaturated Hydrazones/Ketoximes with Diazonium Tetrafluoroborates for Pyridazin-4(1 H )-ones/Oxazin-4(1 H )-ones.

An oxidative 6- endo -trig cyclization and [2 + 2] cycloaddition of β,γ-unsaturated hydrazones/ketoximes and diazonium tetrafluoroborates for a synthetic strategy to pyridazin-4(1 H )-ones/oxazin-4(1 H )-ones under metal-free conditions is presented in a one-pot procedure. This protocol features excellent functional group tolerance and remarkable regioselectivity. A mechanistic study has been verified via 18 O labeling and the H 2 18 O labeling method, in which O 2 acts as both a reaction component and an oxidant.