Alkylidenation and Subsequent Reactions

Many alkylidenehydrazinophthalazines have been isolated, often as intermediates for subsequent cyclization or further elaboration. Although such Schiff bases or hydrazones are usually formulated as such, there is now compelhng evidence that at least some exist as alkylidenehydrazonodihydrophthalazines. Thus X-ray analysis and NMR spectra confirm that l-[A -(l-methoxycarbonylethylidene)hydrazino] phthalazine (115) exists entirely as the tautomeric l-(l-methoxycarbonylethylidene) 

These alkylidenations and some subsequent reactions are illustrated in the following examples. 

4-Dihydrazinophthalazine with salicylaldehyde gave 1,4-bis(salicylidenehy-drazino)phthalazme (129) (EtOH, H2O, reflux, 1 h 90%) that was used (with 

1-Benzylidenehydrazinophthalazine (132) with benzenediazonium chloride gave l,3-diphenyl-5-(phthalazin-l-yl)formazan (133) (reactants, Me2NCHO, 6M HCl, 0°C 2M NaOH dropwise, 2 h 85% analogs likewise). =  

---