Synthesis of Azahelicenes via Friedel‐Crafts‐Type Ring‐Closing Reaction of Axially Chiral Compounds

Aza[6]helicene and aza[7]helicene were synthesized by Fridel‐Crafts‐type cyclization of axially chiral compounds. From the axially chiral compounds prepared by Fischer indole synthesis, aza[6]helicene and aza[7]helicene were synthesized. Aza[7]helicene was also synthesized from an axially chiral pyrrole compound prepared by Piloty‐Robinson‐type pyrrole synthesis through simultaneous cyclization on both sides of the pyrrole ring. Aza[6]helicene isomerized readily at room temperature, while aza[7]helicene isomerization at room temperature was less likely to proceed. The cell growth inhibitory activity of each enantiomer of N‐Me‐aza[7]helicene in HeLa cells was examined. Differences in the strength of activity between the enantiomers were observed.