الفهرس 
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Abstract
It describes the practical details of the reactions of ethyl 5-amino-3,4-diphenylthieno[2,3-c]pyridazine-6-carboxylate 1. This was prepared by reacting 4-cyano-5,6-diphenylpyridazine-3(2H)-thione with ethyl chloroacetate. The amino-ester 1 was allowed to react with phenyl isothiocyanate in boiling pyridine gave thiourea derivative 5, this was cyclized to pyrimido[4`,5`:4,5]thieno[2,3-c]pyridazine derivative 6 using ethanolic potassium hydroxide (Scheme 1). Treatment of compound 6 with hydrazine hydrate produced 6-hydrazino derivatives 7 in 60% yield. On the other hand treatment of the thiourea derivative 5 with hydrazine hydrate produced 7-amino-6-anilino derivative 8 with elimination of hydrogen sulphide molecule. Reaction of 7-amino derivative 8 with p-nitrobenzaldehyde produced the corresponding hydrazone 9, and heating a mixture of 7-amino-6-anilino derivative 8 and triethyl orthoformate in presence of p-toluenesulfonic acid afforded 1,2,4-triazolopyrimido-thienopyridazine derivative 10. When 7-amino-6-anilino derivative 8 treated with NaNO2/AcOH at r.t. gave a single product. The isolated product was proven to be 6-anilino-3,4-diphenylpyrimido[4`,5`:4,5]-thieno[2,3-c]pyridazin-8-one 11 obtained from the N-diazonium ion which generated as an intermediate and ultimate deamination, not the expected tetrazolo derivative 11a as evidence by the analytical and spectral data.