Synthesis and resolution of a new helically chiral azahelicene

Helically chiral azahexahelicene 3 was prepared in four steps using the Mizoroki–Heck coupling followed by classical oxidative photodehydrocyclisation. Resolution of this new chiral system was achieved through separation by HPLC providing (−)- and (+)- 3 in high optical purity. The absolute configurations of (−)- and (+)- 3 were assigned as M and P, respectively, by means of circular dichroism. Each of the hexacyclic systems ( M)-(−)- and ( P)-(+)- 3 was reacted with boron tribromide to provide the corresponding helical pyridophenols in good yields.