n-butyllithium in diethyl ether; hexane byproducts: n-butane, LiCl; addn. of soln. of n-butyllithium in hexane to soln. of isomeric mixture of cyclopentadiene derivative at -78 °C, addn. of ZrCl4 at -78 °C, stirred over night at room temp.; suspn. filtered of Na2SO4, evapn. in vac., washed with n-pentane, dried in vac;