Alk-2-enylpotassium compds. having endo conformation are synthetically very valuable precursors of (Z)-olefinic derivs. substituted at the outward allylic position. They may be generated by \"stereoconservative\" metalation of the readily available (Z)-alk-2-enes by using the superbasic mixt. of BuLi and potassium tert-butoxide or by metalation under similar conditions of stereorandom mixts. of alk-2-enes or alk-1-enes followed by torsional isomerization of the concomitantly formed exo conformers to the thermodynamically more stable endo species. The principal factors that dictate the rate and the extent of the endo/exo equilibration are the substrate geometry, the solvent, the temp., the reagent stoichiometry, and the catalysis. [on SciFinder (R)]