Question

Indicate how each of the following compounds can be synthesized from the given starting material and any other necessary reagents:

Short answer

The reagents used in following synthesis are shown below:

Step-by-step solution

Aldol addition reaction

An aldol addition is a reaction between two molecules of an aldehyde or two molecules of a ketone.Notice that the reaction forms a new Carbon-Carbon bond that connects the α -carbon of one molecule (the nucleophile) and the carbon that was originally the carbonyl carbon of the other molecule (the electrophile). That is, the carbon attached to the OH group is adjacent to the carbon attached to the CHO group.

Claisen Condensation

When two molecules of an ester undergo a condensation reaction, this reaction is known as Claisen condensation.The product of a Claisen condensation is a ß -keto ester.

In a Claisen condensation, one molecule of carbonyl compound is the nucleophile and a second molecule is the electrophile. And, as in an aldol addition, the new C-C bond connects the α -carbon of one molecule of ester to the carbonyl carbon of the other. An alcohol is the small molecule removed in a Claisen condensation.

Crossed Claisen Condensation

A crossed Claisen condensation is a condensation reaction between two different esters. Like a crossed aldol addition, a crossed Claisen condensation is a useful reaction only if it is carried out under conditions that foster the formation of primarily one product.Otherwise, the reaction forms a mixture of products that are difficult to separate. Primarily one product will be formed from a crossed Claisen condensation if one of the esters has no α -hydrogens (and, therefore, cannot form an enolate ion) and the ester with a-hydrogens is added slowly to a solution of the ester without a-hydrogens and the alkoxide ion.

If both esters have a-hydrogens, primarily one product can be formed if LDA is used to removethe α-hydrogen to form the ester enolate ion. The other ester is then added slowly to maximize the chance that it will react with the enolate ion and minimize the chance that it will form an enolate ion and react with another molecule of its parent ester.

Identifying the reagents for the given reactions

All the synthesis of the given starting material are carried out using Aldol, Claisen and Crossed –Claisen Condensation reaction as discussed above in above three steps:

(a) The reagents used in the synthesis of the given products shown below:

(b)The reagents used in the synthesis of the given products shown below:

(c)The reagents used in the synthesis of the given products shown below:

(d)The reagents used in the synthesis of the given products shown below: