in tetrahydrofuran (Ar); dropwise addn. of a soln. of trisubstituted lithium compd. in THF to a suspn. of iron salt in THF at -40°C, stirring for 2 h at room temp., addn. of a soln. of monosubstituted lithium salt in THF at -40°C; evapn., reflux in toluene for 3 h, cooling, filtration, column chromy. (SiO2, toluene/hexane 4:1); elem. anal.;