One‐Pot Synthesis of Helical Azaheptalene and Chiroptical Switching of an Isolable Radical Cation

A nitrogen‐centered heptalene, azaheptalene, was designed as a representative of a new class of redox‐responsive molecules with a large steric strain that originates from the adjacent seven‐membered rings. The pentabenzo derivative of azaheptalene was efficiently synthesized by a palladium‐catalyzed one‐pot reaction of commercially available reagents. Bromination led to mono‐ and dibrominated derivatives, the latter of which is interconvertible with isolable radical cation species exhibiting near‐infrared absorption. Since the azaheptalene skeleton shows configurationally stable helicity with a large torsion angle, enantiomers could be successfully separated. Thus, optically pure azaheptalenes with P‐ or M‐helicity showed strong chiroptical properties (|gabs|≥0.01), which could be changed by an electric potential. A N‐centered helical heptalene, azaheptalene, was synthesized by a palladium‐catalyzed one‐pot reaction. Since the azaheptalene skeleton shows configurationally stable helicity, enantiomers could be successfully separated. Moreover, thanks to the electron‐donating N atom, such helical azaheptalene with two bromine atoms undergoes one‐electron oxidation to produce radical cation species with a drastic chiroptical response.