Hydrogen Bonded Phenol-Quinolines with Highly Controlled Proton-Transfer Coordinate

A series of polycyclic phenols with intramolecular hydrogen bonds (IMHB) to quinolines was synthesized by Friedlander annulation of cycloalkanone-functionalized anisoles with 2-aminobenzaldehyde. The prepared compounds represent the first series of IMHB phenols in which the substitution and conjugation patterns between the phenols and the hydrogen bond acceptors are kept constant, and in which comparable electronic interaction between the two subunits is thus ensured. The distance and relative orientation between the phenolic OH and the quinolone nitrogen atom is controlled by 1,3-cycloalkadienes of different ring sizes to which the phenol and quinoline subunits are formally annulated. H-1 delta(OH) chemical shift and Xray crystal structure characterization support the conclusion that the size and conformational preference of the 1,3-cycloalkadiene rings control the H-bond geometry and strength. As a result, the oxygen to nitrogen distances differ by as much as 0.30ss the seri.