Abstract
Novel fused tricyclic phosphorus heterocycles 9 and 11 and the tetracycle 15 were synthesized by cyclization of 1‐haloalkyl (or 3‐haloalkyl)‐2,3‐dihydro‐1,3,2‐benzodiazaphosphorin‐4(1H)one 2‐oxides with sodium hydride. Some spectral data of the products are also discussed.