Preparation and reactions of 3-phosphinyl-1-aza-1,3-butadienes.: Synthesis of phosphorylated pyridine and pyrazole derivatives

3-Phosphinyl 1-aza-1,3-butadienes 2 are obtained by aldol condensation between hydrazonoalkyl phosphine oxides and N,N-dimethylformamide dimethyl acetal. Transamination reaction of these azadienes with amines yields functionalized 1-aza-1,3-butadienes 3. Cycloaddition processes of these azadienes 2a with electron-poor dienophiles to give phosphorylated pyridine derivatives 9 and 15 are also reported, while intramolecular cyclization reaction of heterodiene 2b affords phosphorylated pyrazole 17. (c) 2005 Elsevier Ltd. All rights reserved.