Polyhalogeno-aromatic compounds. Part IX. Preparation of pentabromophenyl and tetrabromo-4-pyridyl derivatives of lithium and magnesium, and the generation and trapping of tetrabromobenzyne and tribromo-3-pyridyne

Abstract

Metal–halogen exchange between n-butyl-lithium and hexabromobenzene or pentabromopyridine gave pentabromophenyl-lithium and tetrabromo-4-pyridyl-lithium, respectively. Pentabromophenylmagnesium bromide and tetrabromo-4-pyridylmagnesium bromide were prepared from magnesium and hexabromobenzene and pentabromopyridine. respectively, by the entrainment technique. Thermal elimination of metal halide from the organometallic compounds led to tetrabromobenzyne and tribromo-3-pyridyne intermediates. In the presence of benzene, p-di-isopropylbenzene, mesitylene, and 1,2,4,5-tetramethylbenzene, the arynes were trapped as 1,4-adducts; with tribromo-3-pyridyne and mesitylene, a mixture of two isomeric adducts was obtained. Tetrabromobenzyne was also trapped with furan.