Iminophosphoranes in heterocyclic chemistry. A simple one-pot synthesis of pyridothienopyridazines and pyrimidothienopyridazines

Iminophosphoranes, 6-(2-ethoxycarbonylvinyl)-3,4-diphenyl-5-[(triphenylphosphoranylidene)amino]thieno[2,3-c]pyridazine 1a, 6-(2-cyanovinyl)-3,4-diphenyl-5-[(triphenylphosphoranylidene)amino]thieno[2,3-c]pyridazine 1b, and 6-(4-aryliminomethylene)-3,4-diphenyl-5-[(triphenylphosphoranylidene)amino]thieno[2,3-c] pyridazine 5a–c react with heterocumulenes such as iso(thio)cyanates, carbon dioxide and carbon disulfide to give directly the title compounds in an aza-Wittig/electrocyclic-ring closure process. The N-heteroaryliminophosphoranes 8a,b underwent an unusual pyridine ring closure under Vilsmeier conditions to form the pyridothienopyridazines 10a,b.