[5]Helicenes with a substituent exclusively oriented toward the interior curvature of the helix are synthesized by metal-catalyzed cycloisomerization. In addition, novel azulene-fused helicenes have been found through cycloisomerization studies. These [5]helicenes shows a high enough configurationally stability to allow resolution by HPLC on a chiral stationary phase.

Three types of racemic [5]helicenyl acetates (1a, 2, and 3a) were synthesized. The synthesis of 2 was achieved by regioselective oxidation using o-iodoxybenzoic acid. The enzymatic kinetic resolution of 1a-3a was studied. The conversion with the highest rate and ee was obtained using 1a as the substrate and lipase Amano PS-IM as the enzyme. The two enantiomers of 1-[5]helicenol 3b were separated using (1S)-10-camphorsulfonyl chloride as the chiral resolving agent.