Concerning the basicity of 4-dimethylaminoquinazoline derivatives

Two series of selected 4-N,N-dimethylamino-2-phenylquinazoline and 2-N,N-diethylamino-4-N,N-dimethylarnino-quinazoline derivatives obtained in the reaction of substituted N-phenylbenzimidoyl chlorides or N¹,N¹-diethyl-N²-phenylchlorocarboxyamidines with N,N-dimethylcyanamide in the presence of TiCl₄ were examined in order to detect the protonation centre. The untypical correlations between pK_a and σ were supported by MNDO calculations and single crystal X-ray diffraction data and point to a protonation of the ring-N-atoms with delocalization of the positive charge into the N,N-dimethylamino group.