The bromination of saturated 4-alkylamino-N-alkyl-1,8-naphthalimides (e.g 1) proceeds cleanly in halogenated solvents, but several hours are usually required for the complete discharge of the color of the halogen. The first product formed on treating these compounds with bromine is the 3-bromo compound (2); using excess bromine and long reaction times gives the 4-amino compound (3) by dealkylation of the alkylamino group rather than a second ring bromination. In the process of developing site-selective probes for use in fluorescence microscopy of live cells, we needed a dibromide of structure 4, which we expected should be easily obtained by addition of bromine to N-allyl-4-alkylamino-1,8-naphthalimide (5). When one equivalent of bromine was added to a solution of 5 in dichloromethane, the red color persisted for several hours. Reductive work-up of the reaction mixture with sodium sulfite gave two products: a minor product identified as the expected dibromide (4), and the major product, identified as ring-brominated compound 6. The involvement of the heretofore unknown pentacyclic compond 7 was confirmed by single crystal X-ray structure analysis.

Electrophilic aromatic substitution by nucleophiles: Reactions of N-allyl-4-alkylamino-1,8-naphthalimides with halogen-like electrophiles

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