A two‐step synthesis of five 2‐cyanoquinazolin‐4‐ones starting from 3,4,4,5‐tetrachloro‐4H‐1,2,6‐thiadiazine is presented. The latter reacts with 2‐aminobenzamides to give 3′,5′‐dichloro‐1H‐spiro(quinazoline‐2,4′‐[1,2,6]thiadiazin)‐4(3H)‐ones, which can be degraded with either excess polymer bound triphenylphosphine or catalytic amounts of benzyltriethylammonium iodide to give the 2‐cyanoquinazolin‐4‐ones in 46–97% yields. The single crystal X‐ray diffraction analysis of 2‐cyanoquinazolin‐4(3H)‐one is also reported.