Unusual Reactions Between Aromatic Carbon Supernucleophiles and 1,2-Diazabuta-1,3-dienes: Useful Routes to New Pyrazolone and Cinnoline Derivatives

Reactions between 1,3,5-tris(dialkylamino)benzenes and 1,2- diazabuta-1,3-dienes produce semicarbazone derivatives through attack of the supernucleophile aromatic carbon atom at the terminal carbon atom of the heterodiene reagent. The strong activation of the aromatic ring due to the presence of the three amino groups in a symmetrical relationship promotes electrophilic aromatic substitution by the neutral carbon atom of the electrophile. The resulting semicarbazones, in methanol in the presence of sodium methoxide, mainly afford pyrazolone derivatives, whereas in THF in the presence of sodium methoxide an unusual cyclization reaction produces cinnoline derivatives as the major products. Both cyclization reaction mechanisms are discussed.