Na/benzophenone ketyl in tetrahydrofuran byproducts: benzophenone; N2-atmosphere; dropwise addn. of ketyl (stirring, room temp., 45 min); filtering, evapn. (vac.), hexane addn., filtration, concg., crystn. (-78°C, 1 week), washing (hexanes, -78°C), drying (vac.); detd. by (31)P NMR spectroscopy;