Dimerizing or Cyclizing C−C Bond Formation via C−H Bond Activation by Prior Zirconation1

Benzylic hydrocarbons of the types Ar−CH3 and Ar2CH2 undergo zirconation at their benzylic C−H bonds by Bun2Zr(OEt)2 at room temperature in Lewis basic solvents and catalyzed by lithium ethoxide. Upon heating, such benzylic organozirconium derivatives can undergo C−C bond formation, either intermolecularly or intramolecularly, with the elimination of zirconium(IV) hydrides of the type H2Zr(OEt)2. Such oxidative dimerizations or cyclizations are exemplified by the conversion of toluene into trans-stilbene or the formation of 9,10-dihydrophenanthrene from 2,2 '-dimethylbibenzyl.