HBr Cleavage of Cubane-1,4-Dicarboxylic Acid. Easy Entry into theNorthwistbrendane(ene) System

摘要

Addition of hydrogen bromide occurs twice over on heating cubane-1,4-dicarboxylicacid with HBr in HOAc giving in good yield a nortwistbrendane derivative. Further transformations easily give simply substituted nortwistbrendenes. As we are interested in developing the potential of cubanes as starting materials for other valuable systems, we have investigated the course of HBr addition to cubane-1,4-dicarboxylic acid. As anticipated, reaction of 4 with 32% HBr in HOAc at 70 C gives quickly the monoaddition product, characterized as its dimethyl ester. Treatment with aqueous base gives, after acidification, the corresponding lactone, characterized as its methyl ester. Further exposure leads to cleavage of another carbon carbon bond by the addition of a second equivalent of HBr. (No further cleavage occurs on prolonged treatment.) If the second cleavage is similar in kind to the first, there are two reasonable pathways for reaction.