New N-N Bond Cleavage of Fused Chloropyridazines with Ynamines

1-Chlorophthalazine (1) reacts with a 2-fold molar excess of ynamines 2a, b to give penta-substituted pyridine derivatives 3a, b by nitrogen-nitrogen bond cleavage of the pyridazine ring with release of hydrogen chloride. Similarly, other fused pyridazines having a chloro substituent α to nitrogen in the pyridazine ring, i.e., pyrido[3, 4-d]- (10a), pyrido[2, 3-d]- (10b), thiazolo[4, 5-d]- (10c, d), furo[2, 3-d]- (10e) and pyrrolo[2, 3-d]- (10f, g) pyridazine derivatives, gave the corresponding penta-substituted pyridines 11a-11k.