Reaction of the phosphorane (generated using 1 mole of n-BuLi) with an aldehyde at low temperature, followed by a second mole of n-BuLi, gives the -oxido phosphonium ylide which can then be reacted with 1,2-diiodoethane to give (Z)-2-iodo-2-alkenes with high stereoselectivity: J. Chem. Soc., Perkin 1, 1331 (1995).