Synthesis of tribromobenzofuran and tribromobenzopyran derivatives from methyl 2-allyl-4,5,6-tribromo-3-hydroxybenzoate

Palladium(II)-catalyzed oxidative cyclization of methyl 2-allyl-4,5,6-tribromo-3-hydroxybenzoate 4 gave a mixture of methyl 5,6,7-tribromo-2-methyl-benzofuran-4-carboxylate 5 and methyl 6,7,8-tribromo-2H-1-benzopyran-5-carboxylate 6; the ratio of the two products varied between 71:29 and 24:76 depending on the reaction conditions. On the other hand, NBS or NIS mediated cyclization of 4 followed by treatment with NaOMe or DBU furnished benzofuran derivative 5 in good overall yield.