Abstract Monocyclic P–H apical phosphoranes 10 bearing a ring-opened Martin ligand are formed upon treatment of the P–H equatorial spirophosphorane 7 with more than 2 equiv. of alkyllithium compounds. A ligand-exchange process of these phosphoranes 10 involving the interconversion of the bidentate Martin ligand with the monodentate Martin ligand was found to proceed, probably through a hexacoordinate phosphorus atom. Heating of 10 in ...