Helical mesobenzanthrones: a class of highly luminescent helicenes

Diazotization of 3-aminophthalic acid in the presence of 7,9-di(1-naphthyl)-8H-cyclopent[a]acenaphthylen-8-one (9, a dinaphthyl analog of the common cyclopentadienone acecyclone), followed by treatment with thionyl chloride in toluene, gave 11-(1-naphthyl)-7H-fluorantheno[9,8,7-no]tetraphen-7-one (3), an orange luminescent helicene. Similar treatment of 1,3-di(1-naphthyl)-2H-cyclopenta[l]phenanthren-2-one (11, a dinaphthyl analog of phencyclone) gave 11-(1-naphthyl)-7H-triphenyleno[3,2,1-no]tetraphen-7-one (4), a highly luminescent derivative of hexahelicene. Both 3 and 4 are composed of four stable conformational isomers: two diastereomers, each of which contains a pair of enantiomers. One pure isomer of 3 and two isomers of 4 were ultimately obtained by supercritical fluid chromatography (SFC) of the mixtures on chiral supports. These isolated components exhibited high specific rotations and strong circular dichroism. Attempts to prepare a third helicene by diazotization of 3-aminophthalic acid in the presence of aceanthrenecyclone (5) gave no helicene products, but instead resulted in the oxidation of 5 to two unusual chiral diketones (7 and 8) whose structures were determined by X-ray diffraction.

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