Mg(OMe)2 promoted allylic isomerization of gamma-hydroxy-alpha,beta-alkenoic esters to synthesize gamma-ketone esters

This work concerns the Mg(OMe)(2) promoted allylic isomerization of gamma-hydroxy-alpha,beta-alkenoic esters with TMEDA as an additive. The isomerization proceeded under mild conditions and afforded gamma-keto esters in high yield (up to 96%) within 2 h. Both (Z)- and (E)-gamma-hydroxy-alpha,beta-alkenoic esters were tolerated under the reaction conditions. This transformation involves the in situ formation of a dienolate intermediate from the easily accessible gamma-hydroxy-alpha,beta-alkenoic ester. The in situ generated dienolate can react with benzaldehyde and undergo a practical, useful tandem allylic isomerization-Aldol reaction to afford more functionalized compounds.