Methyl 8- and 5-Bromo-1,4-Benzodioxane-2-carboxylate: Unambiguous Identification of the Two Regioisomers

A variety of biological active compounds can be classified as 2-substituted 1,4-benzodioxanes bearing one or more substituents at the benzene. The synthesis of these important templates can be approached by different strategies. The most straightforward ones generally lead to mixtures of positional isomers, whose identification can be more problematic than separation. Here, we unambiguously elucidate, by HSQC and HMBC NMR analyses, the structure of methyl 8- and 5-bromo-1,4-benzodioxane-2-carboxylate, two versatile synthetic intermediates that are one-step-obtainable from commercial products and easily separable. As conceived, the identification procedure is, in principle, generalizable to any pair of 2-substituted 1,4-benzodioxanes bearing an X substituent at C(8) or C(5).