Synthesis and Basicity Studies of Quinolino[7,8- h ]quinoline Derivatives.

Quinolino[7,8-h]quinoline is a superbasic compound, with a pK(aH) in acetonitrile greater than that of 1,8-bis(dimethylaminonaphthalene) (DMAN), although its synthesis and the synthesis of its derivatives can be problematic. The use of halogen derivatives 4,9-dichloroquinolino [7,8-h] quinoline (16) and 4,9-dibromoquinolino [7,8-h]quinoline (17) as precursors has granted the formation of a range of substituted quinolinoquinolines. The basicity and other properties of quinolinoquinolines can be modified by the inclusion of suitable functionalities. The experimentally obtained pK(aH) values of quinolino[7,8-h]quinoline derivatives show that N-4,N-4,N-9,N-9-tetraethylquinolino[7,8-h] quinoline-4,9-diamine (26) is more superbasic than quinolino[7,8-h]quinoline. Computationally derived pK(aH) values of quinolinoquinolines functionalized with dimethylamino (NMe2), 1,1,3,3-tetramethylguanidino (N=C(NMe2)(2)) or N,N,N',N',N ",N "-hexamethylphosphorimidic triamido (N=P(NMe2)(3)) groups are significantly greater than those of quinolino [7,8-h] quinoline. Overall, electron-donating functionalities are observed to increase the basicity of the quinolinoquinoline moiety, while the substitution of electron-withdrawing groups lowers the basicity.