Ms. South et Tl. Jakuboski, SYNTHESIS AND REACTIONS OF CHLOROAZODIENES - A NEW AND GENERAL-SYNTHESIS OF PYRIDAZINES, Tetrahedron letters, 36(32), 1995, pp. 5703-5706
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.