Halogen – metal exchange of 3-substituted 1,2-dibromoarenes: the use of long-rangeJCH 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 H-1 coupled C-13 experiments, were necessary to render unequivocal regio assignments. Copyright (c) 2006 John Wiley & Sons, Ltd.