Oxidative addition of a quinone to a cyclic phosphite gave a nearly quantitative yield of a bicyclic tetraoxyphosphorane. Contrary to the electronegativity rule governing positional preferences for a main group element in a trigonal bipyramidal geometry, the least electronegative ligand, a phenyl group, is located at an axial site as shown by X-ray analysis. The ease of occupancy of diequatorial positions by a flexible eight-membered ring is offered as a rationale for this occurrence.