Mild Base-Promoted Indole Annulation-Oxidative Cross- Coupling of 2-Nitrocinnamaldehydes with -Tetralones for 3-Naphthylindole and 3-Naphthylbenzo[g]indole Fluorophores

This paper describes the transition metal-free indole annulation-oxidative cross-coupling of 2-nitrocinnamaldehydes or (E)-3-(1-nitronaphthalen-2-yl)acrylaldehyde with -tetralones for the construction of diverse 3-naphthylindole and 3-naphthylbenzo[g]indole fluorophores in moderate to good yields. This unique annulation reaction proceeds via the domino Michael addition/hemiacetalization/intramolecular addition of an enolate to a nitro group/decarbonylation/oxidative aromatization sequence under transition metal-free conditions without the use of an external reductant and oxidant. The synthetic utility of this protocol has been also demonstrated by evaluating the photophysical properties of the synthesized 3-naphthylindole and 3-naphthylbenzo[g]indole derivatives.