Helicenes are ortho-condensed aromatic compounds with helical structures, which have received considerable attention because of unique helical non-planar p-electron system and of their very high rotational values. The helicenes containing more than six benzene rings (carbohelicenes) or seven heteroaromatic rings (heterohelicenes) possess rigid helical framework and are very stable toward acids, bases, and relatively high temperature. Especially, chiral functionalized analogues are promising candidates for chiral ligands and auxiliaries in asymmetric syntheses.
We have recently found that 2,13-bis-(hydroxymethyl)dithieno[3,2-e:3',2'-e']benzo[1,2-b:4,3-b']bis[1]benzothiophene
(1) interacts with guest molecules such as ethanol, 1,2-dichloroethane and
testosterone to form crystalline inclusion complexes with a variety of
host-guest stoichiometric ratios. The X-ray analysis of the inclusion complexes
indicates that the dihedral angle between terminal thiophene rings of helicenediol
1 in the clathrates varies from 38.0º for (PM-1)·(EtOH) to 54.5º for (PM-1)·(1,2-dichloroethane)0.5. These results indicate that the helical conjugated
p-electron framework of 1 elongates
and contracts as a "spring".
We are now studying on the synthesis and properties of chiral
functionalized heterohelicenes.
