6-Ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone

The Robinson annulation of ethyl acetoacetate and trans-chalcone proceeded smoothly to give 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone in 48 % yield. The product was separated from the ionic liquid by solvent extraction with toluene. In both these reactions, the ionic liquid [HMIM][PF6] was recycled and reused with no reduction in the product yield. 

The Robinson annulation of ethyl acetoacetate and tra i -chalcone was investigated with pulverized NaOH in [BMIMjPFg as the base catalyst at 100°C 110). The mixture was neutralized before extraction with toluene. The product, 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone, was obtained by purification in a silica gel chromatography column. A yield of 48% was obtained (Scheme 7). The ionic liquid could be recycled and reused with no diminution of product yield. The C2 position in imidazolium cations is an acidic proton donor and may have reacted... 

This experiment illustrates how two important synthetic reactions can be combined to prepare an a,)8-unsaturated ketone, 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone. The first step in this synthesis is a sodium hydroxide-catalyzed conjugate addition of ethyl acetoacetate to transchalcone (a Michael addition reaction). Sodium hydroxide serves as a source of hydroxide ion to catalyze the reaction. In the reactions that follow, Ph and Et are abbreviations for the phenyl and ethyl groups, respectively. 

Draw a mechanism for each of the three steps in the preparation of the 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone. You may assume that sodium hydroxide functions as a base and ethanol serves as a proton source. 

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