The [1+1] cyclocondensation of the bis-PCl species 1,2-bis(benzo-1-methyl-2-chloro- 1,3,2-diazaphosphorin-4-on-3-yl)ethane 1 and 1,3-bis(benzo-1-methyl-2-chloro-1,3,2-diazaphosphorin- 4-on-3-yl)propane 2 with the 1,2-benzenediol bis(trimethylsilyl) ether 3a and 2,3- naphthalenediol bis(trimethylsilyl) ether 3b gave the symmetrical phosphorus-containing largering systems 4 - 7 in moderate yield. The phosphoryl compounds 8 - 11 were obtained by the oxidation of 4 - 7 with (H2N)2C(:O) H2O2. Oxidation of 6 and 7 with elemental sulfur furnished the thiophosphoryl compounds (12 and 13). All new compounds formed in the reactions were characterized unambiguously by NMR spectroscopy, mass spectrometry, and elemental analysis. For compounds 6, 9, 10, 11 and 12, X-ray crystal structure determinations were conducted. The compounds with ten-membered rings show approximate (6, 12) or exact (10) twofold symmetry. In each of the compounds 9 and 11 the two six-membered heterocycles are appreciably different; one is approximately planar, whereas in the other, phosphorus lies outside the plane of the other five atoms