Preparation of Stable Primary Enamines: 1-Aminobutadienes by Allyl Grignard Addition to Aryl Cyanides Followed by Controlled Hydrolysis

Article abstract of DOI:10.1021/jo00121a055

From thermochemical data it is suggested that 1-aminobutadienes are more stable than their nonconjugated imine tautomers by about 2 kcal mol^-1.High level ab initio calculations have established the thermodynamic preference of the conjugated primary enamines over their β,γ-unsaturated ketimine isomers in the gas phase.This general prediction of an increased stability of primary enamines by butadiene conjugation has been confirmed experimentally with a variety of representative examples.Allyl Grignard addition to a number of aryl or hetaryl cyanides followed by controlled hydrolysis yields the respective β,γ-unsaturated ketimine systems that subsequently rearrange completely to their 1-aminobutadiene isomers.Rearrangement to the thermodynamically more favored α,β-unsaturated imine tautomers is kinetically inhibited and, hence, not observed in these systems.In some cases conjugated enamine formation is already observed at the stage of the organometallic intermediates.