Lithiation of toluene by organolithium compounds activated by lithium polyether alkoxides

The catalytic effect of polyether alkoxides (PEAs) on the activity of organolithium. compounds as metallating agent has been investigated. Toluene has been lithiated by using different organolithiums activated by various PEAs. It has been found that n-BuLi, yields higher conversion with 100% benzylic position metallation, whereas sec-BuLi gives some metallation at ring positions with the most reactive ligand, lithium 2-methoxy ethoxide (LiOEM). Optimum PEA to organolithium molar ratio for both sec- and n-BuLi activated by LiOEM where the amount of toluene being kept constant, was found to be as 3:1 with highest yield and regioselectivity. Substantial increment in yield was observed when the amount of substrate increased whereas regioselectivity stayed almost constant. It was also found that, for a constant reactant molar ratio (3:1:15) for which the optimum results were achieved, reaction began early and then yield values increased with time whereas upon increase in reaction temperature from -78 to 20degreesC, the benzylic metallation yield increased drastically while keeping the same regioselectivity high.