The synthesis of small-ring heterocycles containing phosphorus, including phosphetans and phosphirans, by a variety of conventional methods, as well as by reactions involving highly reactive intermediates produced by high-energy processes like arc reactions, is being studied. Spectral and structural studies on these compounds, and on intermediates in their syntheses, are under way. The use of complexes of primary and secondary phosphines in template reactions designed to prepare polyfunctional phosphorus ligands is being examined. Other approaches to such ligands are also being undertaken, including high-dilution cyclization reactions of suitable difunctional precursors.