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

Quinolino[7,8- h ]quinoline is a superbasic compound, with a p K _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 p K _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 p K _aH values of quinolinoquinolines functionalized with dimethylamino (NMe ₂ ), 1,1,3,3-tetramethylguanidino (N═C(NMe ₂ ) ₂ ) or N , N , N ', N ', N ″, N ″-hexamethylphosphorimidic triamido (N═P(NMe ₂ ) 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.