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 Superba ses, prepared from butyllithium (BuLi) and potassium tert-pentoxide (t -PeOK), affects the metallation rate of toluene only slightly, the rat e factors being between 1.0 and 0.3. Thus, lithium alkoxide is not ess ential for the high reactivity of Superbases. However, the ring-to-sid e 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 greater-t han-or-equal-to 3) considerably increases the rate and yield of the si de chain metallation of toluene and suppresses its ring metallation. I n this way, alkoxides enable some control on regioselectivity in Super base reactions