Expanded [2,1][n]Carbohelicenes with 15-and 17-Benzene Rings

Expanded carbohelicenes with structures fused to 15-and 17-benzenewere successfully synthesized. Establishing a new synthetic strategyis crucial to realize the development of longer expanded [2,1]-[n]-helicenes with a kekulene-like projection drawing structure.This article describes the sequential integration of the pi-elongatingWittig reaction of functionalized phenanthrene units and ring-fusingYamamoto coupling for the synthesis of [2,1][15]-helicenes and [2,1][17]-helicenes.X-ray crystallographic structures, photophysical properties, and densityfunctional theory (DFT) calculations revealed the unique characteristicsof the synthesized expanded helicenes. Furthermore, because of thehigh enantiomerization barrier derived from a wide-range intrahelix pi-pi interaction, the optical resolution of [2,1][17]-helicenewas successfully achieved, and chiroptical properties such as circulardichroism and circularly polarized luminescence were elucidated forthe first time as enantiomers of pristine [2,1]-[n]-helicene core.