Pyrene‐Fused Furan: Simple Synthesis of π‐Expanded Heterohelicene

Abstract Treatment of p ‐toluenesulfonic acid on bipyrenol in PhCl gave a pyrene‐fused furan. The expansion of the molecule induced a narrow HOMO‐LUMO gap, multiple redox processes showing both oxidation and reduction, and a bathochromic shift in the absorption spectrum. A small Stokes shift was caused by the rigidity of the molecule. The structures and electronic states were estimated by theoretical considerations. We found that the heteroatom containing a [5]helicene molecule shows racemization through a planar transition state.