Electrophilic Substitution in 5,6-Bis(dimethylamino)acenaphthylene as a Route to Push-Pull Proton Sponges

Unlike 1,8-bis(dimethylamino)naphthalene (pro ton sponge), 5,6-bis(dimethyl - amino)acenaphthylene 2 has been shown to undergo H/D-ex change in CF3CO2D at 65°C. Both hydrogen atoms at the C1=C2 double bond and inpositions 3(8) and 4(7) of the naphthalene fragment are reactive in the ratio 3:1.3:1, respectively. Arylsulfonation and nitration of 2 with tetranitromethane provide direct substitution at C(1) with the formation of push-pull derivatives in moderate yield. Isomeric 3-ni tro- and 4-ni tro- 5,6-bis(dimethylamino)acenaphthylenes can be synthesized via dehydrogenation of their more accessible acenaphthene precursors. The Vilsmeier formylation of 2 affords along with 1-formyl- and 1,2-diformyl derivatives some amount of 1,7-dialdehyde that reflects a comparable reactivity of ethylene and naphthalene moieties in the non-protonated substrate. The green ish-yel low proton salt of deep violet 5,6-bis(dimethyl amino)acena -phthylene-1,2-dicarbaldehyde has been found to exhibit strong positive solvatochromism caused by partial deprotonation.