Spontaneous Helix Formation of " meta"-Ethynylphenol Oligomers by Sequential Intramolecular Hydrogen Bonding inside the Cavities

Phenol-based oligomers linked with acetylenes at their meta positions, "meta"-ethynylphenol oligomers, were developed as a synthetic helical foldamer. The architecturally simple oligomers spontaneously formed helical higher-order structures by sequential intramolecular hydrogen bonds through the multiple phenolic hydroxy groups inside the cavities. The hydrogen bonds forced C-C≡C-C bond angles to largely bend toward the inside. Addition of chiral amines caused the helices to be chiral by electrostatic interactions between the resulting chiral ammonium cations and the phenolate anions.