Five, six, and seven-membered phosphorus heterocycles containing "O- P-O" or "N-P-N" or "N-P-O" bonds were synthesized using cyclization reactions of Lawesson's reagent with bifunctional compounds containing mobile hydrogens. A cyclization mechanism was also proposed. The results of preliminary bioassays show that phosphorus heterocycles prepared have good selective herbicidal activity.

Key words: HERBICIDES, BIOLOGICAL ACTIVITY, PHOSPHOROUS HETEROCYCLIC COMPOUNDS, CYCLIZATION, SULPHIDIZER, DUAL FUNCTIONAL GROUP