Conformations of 1,3,6,2-dioxaselenaphosphocanes

4,8-Dimethyl-2-phenyl-1,3,6,2-dioxaselenaphosphocane 2-selenide 6 was synthesized by the condensation of dichlorophenylphosphine and 4-selenaheptane-2,6-diol 8 followed by oxidation with selenium. The conformations of 6 and related 2-(p-methylphenoxy)-1,3,6,2-dioxaselenaphosphocane 2-oxide 7 in the solid state and in solution were studied through X-ray diffraction and NMR spectroscopy. The asymmetric boat–chair conformation in both solid state and solution was established for the eight-membered heterocycles.