The effect of lithium alkoxides on deprotonizations by superbases made from butyllithium and potassium tert-pentoxide
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.