Selective mono- or dimetalation of arenes by means of superbasic reagents

If employed in THF, stoichiometric amts. of BuLi and KOCMe3 react with benzene to give clean monometalation. In hexane suspension, however, considerable amts. of meta and para-disubstituted byproducts are obtained (approx. 10%). They become preponderant if a 3-fold excess of the metalating agent is used. Naphthalene, under the same conditions, gives a mixt. of two mono- and ten disubstituted derivs. Alkyl groups, as present in tert-butylbenzene, retard the metalation at both m- and p-positions, while trialkylsilyl groups deactivate only m-positions. In either case exclusive monosubstitution occurs. Perdeuteriobenzene undergoes metalation and subsequent electrophilic mono- or disubstitution to afford isotopically labeled compds. with moderate, though synthetically attractive yields. The kinetic isotope effects and product ratios can be taken as evidence for aggregate formation at the level of both the superbasic metalating reagent and the organometallic intermediates. [on SciFinder (R)]