A Stereoselective Synthesis of (E)‐α, β‐Unsaturated Ketones Involving the Reactions of Organocerium Reagents with Secondary β‐Enamino Ketones

Abstract

AbstractStereoselective construction of trisubstituted alkenes has wide applicability to the synthesis of many natural products Specifically, β‐disubstituted enones are important functionalized trisubstituted alkene targets. The reaction of organocerium reagents with secondary β‐enamino ketones affords β=disubsituted α,β‐unsaturated ketones in fairly good yields. This process shows considerable stereoselectivity, and α,β‐unsaturated ketones of (E) configuration are predominantly observed. Organolithium‐derived cerium reagents display better stereoselectivity than organomagnesium‐based ones. The mechanism of the reaction varies with nitrogen substitution: N‐phenyl groups give 1,2‐addition products, whereas substitution products are observed with N‐alkyl groups. When organocerium reagents were used with β‐enamino ketones bearing secondary alkyl groups at the nitrogen atom, a lack of reactivity was observed.