5,6-Bis(dimethylamino)acenaphthylene as an activated alkene and ‘proton sponge’ in halogenation reactions

Abstract

It has been shown that 5,6-bis(dimethylamino)acenaphthylene in its reactions with X 2 (X=Cl, Br, I) and N-X-succinimides behaves simultaneously as an electron-rich alkene or arene and proton sponge. Thus, addition of bromine or iodine to the C(1) C(2) bond is followed by immediate dehydrohalogenation leading to the formation of the corresponding 1(2)-(di)halogenoacenaphthylenes in good yields. Reaction with chlorine enables isolation of only 1,4,7-trichloro-5,6-bis(dimethylamino)acenaphthylene. With N-halosuccinimides, the halogenation is directed mainly by the steric bulk of the entering halogen and then by solvent polarity thus allowing the regioselective preparation of 1(2)- or 4(7)-(di)halides. Introduction of the third and fourth bromine atoms, but not chlorine, is accomplished by mono-N-demethylation. The p K a values of some new derivatives of acenaphthene and acenaphthylene proton sponges were measured by competitive transprotonation 1H NMR spectroscopy technique in DMSO. The X-ray molecular structures of 4,7-dichloro-5,6-bis(dimethylamino)acenaphthylene and its monoprotonated form are reported.