Collect. Czech. Chem. Commun. 1993, 58, 1445-1451

The Effect of Lithium Alkoxides on Deprotonizations by Superbases Made from Butyllithium and Potassium tert-Pentoxide

Lubomír Lochmanna, Hana Jakubůva and Lambert Brandsmab

a Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic
b Department of Preparative Organic Chemistry, University of Utrecht, 3584 CH Utrecht, The Netherlands


The presence or absence of lithium tert-pentoxide (t-PeOLi) in Superbases, prepared from butyllithium (BuLi) and potasium tert-pentoxide (t-PeOK), affects the metallation rate of toluene only slightly, the rate factors being between 1.0 and 0.3. Thus, lithium alkoxide is not essential for the high reactivity of Superbases. However, the ring-to-side chain metallation ratio is increased in the presence of t-PeOLi. On the other hand, an excess of t-PeOK (molar ratio t-PeOK/BuLi ≥ 3)considerably increases in the rate and yield of the side chain methallation of toluene and suppresses its ring mrtallation. In this way, alkoxides enable some control on regioselectivity in Superbase reactions.