Synthesis of (E)-1-Propenyl Ketones from Carboxylic Esters and Carboxamides by Use of Mixed Organolithium-Magnesium Reagents. Synthesis of α-Damascone, β-Damascone,and β-Damascenone

The novel reagents formed by combination of allylmagnesium chloride and a strong non-nucleophilic lithium base (LiNR₂) convert non- or slowly enolizable carboxylic esters or carboxamides into 2-propenyl ketones which are protected from further reaction by their in situ conversion into enolates. This modified Grignard reaction is applied to efficient syntheses of α-damascone, β-damascone, β-damascenone, and various other (E)-1-propenyl ketones.