SELECTIVE MONO- OR DIMETALATION OF ARENES BY MEANS OF SUPERBASIC REAGENTS

Article abstract of DOI:10.1016/S0040-4020(01)87763-2

If employed in tetrahydrofuran, stoichiometric amounts of butyllithium and potassium tert-butoxide react with benzene under clean monometalation.In hexane suspension, however, considerable amounts of meta- and para-disubstituted by-products are obtained (approx. 10percent).They become preponderant if a three-fold excess of the metalating agent is used.Naphthalene leads under the same conditions to a mixture of two mono- and ten di-substituted derivatives. - Alkyl groups, as present in tert-butylbenzene, retard the metalation at both m- and p-positions, while trialkylsilyl groups deactivate only m-position.In either case exclusive monosubstitution occurs. - Perdeuterobenzene undergoes metalation and subsequent electrophilic mono- or disubstitution to afford isotope labeled compounds 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.