Metal‐Free [4 + 2] Annulation of Arylalkynes with tert‐Butyl Nitrite Through C(sp2)—H Oxidation to Assemble Benzo[e][1,2]oxazin‐4‐ones.

A metal-free radical-mediated [4+2] annulation of internal arylalkynes with tert-butyl nitrite (t-BuONO) is presented for the synthesis of benzo[e][1,2]oxazin-4-ones through the addition of t-BuONO across the C C triple bond, hydration, isomerization and aromatic C(sp(2)) H oxidation cascades. The O-18-labeling experiment shows that two oxygen atoms in the product system are from water.