SYNTHESIS AND REACTIONS OF CHLOROAZODIENES - A NEW AND GENERAL-SYNTHESIS OF PYRIDAZINES

The reaction of dichlorohydrazones with Hunig's base gives 4-chloroazo dienes, which were found to combine with a variety of electron rich ol efins to yield chloro-substituted tetrahydropyridazines. These chloroa zodiene cyclizations are best characterized as inverse electron demand , 4+2 hetero Diels-Alder reactions that maintain a high degree of regi o- and stereochemical control. The chloro-substituted tetrahydropyrida zines that are formed give high yields of substituted pyridazines upon treatment with base. The sequence of a chloroazodiene cyclization to a tetrahydropyridazine followed by an aromatization constitutes a new and general synthesis of substituted pyridazines.