Reactions of 2-Bromo-3-Methoxy-1,4-Naphthoquinone with Diaminoalkanes

Abstract

The reactivity of 2-bromo-3-methoxy-1,4-naphthoquinone toward diaminoalkanes is studied here. We reacted 2-bromo-3-methoxy-1,4-naphthoquinone with the following diaminoalkanes: ethylenediamine, 1,3-diaminopropane, N-methylethylenediamine, N-acetylethylenediamine, and 2-aminoethanol. In the reaction of 2-bromo-3-methoxy-1,4-naphthoquinone with ethylenediamine, for example, we isolated 2-2?-aminoethylamino-3-bromo-1,4-naphthoquinone as the major product. We also reacted our starting quinone, 2-bromo-3-methoxy-1,4-naphthoquinone, with the salts of these diaminoalkanes. We expected the salt form of the amine would behave the same as the free amine after the salt?s being freed in the presence of a base. Actually, we found that the freed form of the salt form of some diaminoalkanes produced the product more cleanly in a higher yield. The mechanism for these reactions was also interesting because a substitution occurred at the 3-methoxy site. This is unusual because a bromine atom is a much better leaving group than a methoxy group in a nucleophilic substitution process. We examined a variety of solvents including methanol, ethanol, and chloroform. We also studied the reactions of 3-methoxy-1,4-naphthoquinone with these amines in order to examine the role of the bromine atom in our reaction.