Vinylamines. Part IX. Reaction of cyclohexanone enamines with αβ-unsaturated ketones

Abstract

The two-step mechanism for the formation of dihydropyrans from enamines and αβ-unsaturated ketones is established on the basis of the results of the reaction of 1-morpholinocyclohexene with cis- and trans-dibenzoylethylene. The dihydropyran derivative obtained from the same enamine and chalcone undergoes thermal rearrangement affording almost exclusively the less substituted alkylated enamine. A mixture of less (48%) and more substituted (52%) alkylated enamine is obtained when the dihydropyran derivative from 1-morpholinocyclohexene and phenyl vinyl ketone is heated. The mechanism of the two different rearrangements is discussed.