Novel homologation reaction of arylzincates bearing a leaving group at the ortho and meta positions

Arylzincates bearing a leaving group at the ortho, meta, and para positions were generated by iodine/zinc exchange reaction of the corresponding iodoaryl sulfonates with Bu3ZnLi, and their reactivity was investigated via product analysis after hydrolysis and treatment with iodine. Zincates derived from o-iodophenyl triflates and tosylate underwent homologation reaction to give o-butylphenylzinc species. o-Benzyne as an intermediate of the reaction was demonstrated by the lack of regioselectivity for trisubstituted zincates. Zincates derived from m-iodophenyl triflates also underwent homologation leading to m-butylphenylzinc species. Similar product ratios observed in the reactions of regioisomeric trisubstituted iodophenyl triflates as well as the formation of radical reaction byproducts suggested the involvement of rn-benzyne intermediate. p-(Trifluoromethane-sulfonyloxy)phenylzincate was thermally stable at room temperature; generation of p-benzyne was not observed.