Enamine chemistry. Part IX. Synthesis, structure, and spectra of acyclic dienamines; linear versus cross-conjugation

Abstract

The mode of reaction of acyclic αβ-unsaturated ketones with secondary amines has been shown to depend upon the substituents present in the ketone. With αβ-unsaturated ketones containing one C(β)-substituent, either amine addition to the carbon–carbon double bond occurs, or the linear dienamine is formed. When an additional C(α)-substituent is present only the cross-conjugated dienamine is formed. The presence of two C(β)-substituents results in the formation of an equilibrium mixture of linear and cross-conjugated dienamines, the latter being the more stable thermodynamically. The stereochemistry and spectra of the dienamines and of the corresponding unsaturated ketones formed on hydrolysis are reported, and the course of the conversion of methyl alkyl ketones, and of their monoenamines, into dienamines is discussed.