Conjugate Addition to 1-Phosphono-2-aza-1,3-butadienes:Synthesis of Phosphonylated gamma-Lactams

摘要

Several 1-phosphono-2-aza-1,3-butadienes,1 and 13-20,were evaluated in the reaction with different enolate-type nucleophiles to induce addition at the 1-or the 4-position of the azadiene.1-Phosphono-2-azadienes 1 react with sodium malonate at the 1-position,leading to the formation of bisenamines 12 after elimination of the phosphonate moiety.On the contrary,sodium malonate adds at the 4-position of l-aryl-1-phosphono-2-azadienes 14-19 when the azadienes bear a halogenated phenyl substituent,and the resulting addition products 21-26 are easily transformed into the corresponding phosphonylated gamma-lactams 35-40.The regioselectivity of the addition is explained by reversal of polarization of the azadiene due to the electron-withdrawing character of the halogenated phenyl substituents.