Reactions of allene with amines and active methylene compounds; adduct formation in the presence of nickel complexes

Abstract

Reactions of morpholine, pyrrolidine, di-n-propylamine, aniline, and n-butylamine with allene in the presence of a nickel salt and di-isopropoxyphenylphosphine have been studied. Mixtures of 1 : 1, two 1 : 2, and two 1 : 3 amine-allene adducts were formed, and with the exception of n-butylamine, the 1 : 3 adducts constituted >50% of the product amines. An essentially analogous reaction occurred with the active methylene compounds, diethyl malonate, ethyl acetoacetate, benzyl cyanide, and benzyl methyl ketone with the preferential formation of 1 : 3 adducts; the inclusion of either sodium phenoxide or sodium borohydride to the catalyst system was found necessary for reaction. The mechanism has been interpreted in terms of a 1 : 1 and 2 : 1 allene-nickel intermediate and a 3 : 1 allene–bisallyl-nickel intermediate. The specificity of reaction has been suggested to be a consequence of the σ, π character of the bis-π-allylnickel complex with preferential reaction of the nucleophilic active hydrogen compound at a π-allylnickel bond.