Carboxylic Acids with a Carbonyl Group at the 3-Position Can Be Decarboxylated

To determine the starting materials needed for the synthesis of a 2-cyclohexenone by a Robinson annulation, first draw a line that bisects both the double bond and the (T bond between the jS- and y-carbons on the other side of the molecule. The 8-carbon comes from the o ,jS-unsaturated carbonyl compound the y-carbon is the a-carbon of the enolate ion of the second carbonyl compound that will add to the 8-carbon in the Michael reaction. The double bond was formed by the reaction of the enolate ion of the o , S-unsaturated carbonyl compound and the carbonyl carbon of the second carbonyl compound. 

By cutting through the following compound in the same way, we can determine the required reactants for its synthesis  

What two carbonyl compounds are needed to synthesize each of the following confounds, using a Robinson annulation  

17 CARBOXYLIC ACIDS WITH A CARBONYL GROUP AT THE 3-POSITION CAN BE DECARBOXYLATED 

Carboxylate ions do not lose CO2, for the same reason that alkanes such as ethane do not lose a proton— namely, the leaving group would be a carbanion. Carbanions are very strong bases, which makes them very poor leaving groups. 

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Carboxylic Acids with A Carbonyl Group at the 3-Position Can Be Decarboxylated 883... 

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