Reactions of active methylene compounds with 1,3-dienes catalysed by nickel complexes

Abstract

Reactions of buta-1,3-diene with benzyl methyl ketone, benzyl cyanide, diethyl malonate, and ethyl acetoacetate have been studied in the presence of nickel salts, di-isopropoxyphenylphosphine, and a cocatalyst such as sodium phenoxide. Mixtures of 2 : 1 and 1 : 1 adducts were obtained with the former in predominant quantities. Nickel halides provided the most active catalyst system and the product ratio could be affected by the concentration of reagents and phosphine. Mainly 1 : 1 adduct was obtained on reaction of isoprene with benzyl methyl ketone and exclusive formation of this adduct was found with 2,3-dimethylbutadiene and piperylene. The reaction has been suggested to occur by competing processes involving π-allylnickel and bis-π-allylnickel complexes leading to 1 : 1 and 2 : 1 adducts, respectively. Reactions with diethyl malonate and ethyl acetoacetate require higher amounts of the nickel system which has been demonstrated to be due to complex formation between the catalyst and reagents. The importance of cocatalysts such as sodium phenoxide has been stressed.