The Proton Sponge Effect: Substitution of Quino[7,8-h]quinoline and the First Structurally Characterised Derivatives

A new route to unsymmetrical derivatives of quino[7,8-h]quinoline was developed. Substitutions at the 2,11-, 4,9- and 6,7-positions of quino[7,8-h]quinoline were also successfully performed. X-ray crystal structure determinations of the resulting products revealed the propensity for derivatives of this molecule to exist in either stabilised keto or imino forms as a result of the formation of a strong intramolecular N–H···N hydrogen bond.