Synthesis of Polycation-type Helicenes with Electron-accepting Properties for Stereoselective Molecular Recognition

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Two types of azonia-helicenes, in which a carbon atom of the middle and inner helix skeleton is replaced by a quaternary nitrogen atom, were synthesized by the use of three-types photocyclization : (A) photocyclization of 1-styrylpyridinium salts to benzo[a]quinolizinium derivatives, (B) photocyclization of styrylquinolizinium salts to fused azonia compounds, (C) photocyclization of 2-styrylpyridine derivatives to benzo[c]quinolizinium salts. Helicenes with azonia-nitrogen at the middle helix skeleton were synthesized by the use of types A and B.Irradiation (type A) of 4-methyl-1-[2-(2-naphthyl)vinyl]pyridinium salt in methanol led to 2-methylnaphto[1,2-a]quinolizinium salt(1). The condensation reaction of 1 with benzaldehyde derivatives in the presence of piperidine in acetonitrile gave the corresponding styryl derivatives (2). The styryl derivatives (2) were photocyclized in the presence of iodine by the irradiation with a Pyrex-filtered light to afford the desired azonia[6]helicenes with a quaternary nitrogen at the middle helix skeleton.The reaction of benzo[h]quinoline and 1,10-phenanthroline with methyl lithium in toluene gave the corresponding 2-methyl derivatives. The methyl derivatives reacted with 1-chloro-2-formyl-naphthalene in refluxing acetic anhydride to afford the corresponding olefins. New 16c-azonia[6]helicenes with a quaternary nitrogen at the inner helix skeleton were obtained by photoinduced intramolecular quternization of the olefins in acetonitrile.