A parallel method for the synthesis of the title compounds is described. Thus, methyl anthranilates (5) are transformed into 2-aminobenzohydrazides (3) which were treated with 4-oxo acids (4) to afford in high yields and acceptable purity of piridazino[3,2-b]quinazolines (1). Compounds (1) present four diversity centers (R1, R2, R3, and R4). The range of chemically acceptable substituents at each center has been evaluated. The isolation of a possible intermediate in the formation of 1, which presents an amino structure (10), has allowed proposing a complete mechanistic rationalization for the formation of structures (1).