Three novel helical dications (helquats) containing phenanthridinium units have been
synthesized from 6-(pyridin-2-ylethynyl)phenanthridine as a common precursor prepared
by Sonogashira coupling of phenanthridin-6-yl triflate with 2-ethynylpyridine. Bisquaternization
of the common precursor followed by rhodium-catalyzed [2+2+2] cycloisomerization led
to the title helical dicationic scaffolds. The connectivity and spatial arrangement
of the three target helquats were unambiguously established by X-ray crystal structure
analysis.
Key words
helical structures - rhodium - catalysis - cycloadditions - heterocycles - Sonogashira
coupling - helquats - heteroaromatic cations