Halogen-metal exchange of 3-substituted 1,2-dibromoarenes: The use of long-range J_CH coupling constants to determine regiochemistry

Regioselective halogen/metal exchange reactions were carried out on a series of 3-substituted-1,2-dibromoarenes. Product mixtures were quenched with CO₂ to form the corresponding benzoic acid analogs to facilitate HPLC and NMR analysis. Substitution at the 3-position could readily be assigned on the basis of 2D HMBC long-range correlations, while assignment at the 2-position was not as straightforward. The use of three-bond J_CH coupling constant measurements, extracted from 1-D ¹H coupled ¹³C experiments, were necessary to render unequivocal regio assignments.