Synthesis of 2‐Cyanoquinazolin‐4‐ones from 3′,5′‐Dichloro‐1 H ‐spiro(quinazoline‐2,4′‐[1,2,6]thiadiazin)‐4(3 H )‐ones

A two‐step synthesis of five 2‐cyanoquinazolin‐4‐ones starting from 3,4,4,5‐tetrachloro‐4 H ‐1,2,6‐thiadiazine is presented. The latter reacts with 2‐aminobenzamides to give 3′,5′‐dichloro‐1 H ‐spiro(quinazoline‐2,4′‐[1,2,6]thiadiazin)‐4(3 H )‐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(3 H )‐one is also reported.