Claisen & Dieckmann Condensation Reference Cheat Sheet

Key Facts

• A Claisen condensation joins two ester molecules to form a $\beta$-keto ester after base treatment and acidic workup.
• The general Claisen pattern is $2\ \mathrm{RCOOR'} \xrightarrow{\mathrm{R'O^-}} \mathrm{RCOCH_2COOR'} \xrightarrow{\mathrm{H_3O^+}} \beta\text{-keto ester}$.
• The base should match the ester alkoxy group, such as using $\mathrm{EtO^-}$ with an ethyl ester, to avoid transesterification.
• A Claisen condensation needs at least one ester with $\alpha$-hydrogens so an enolate can form at the $\alpha$-carbon.
• A Dieckmann condensation is an intramolecular Claisen reaction of a diester that forms a cyclic $\beta$-keto ester.
• Dieckmann cyclizations usually favor formation of $5$-membered and $6$-membered rings because those rings have lower strain.
• After condensation, acidic workup with $\mathrm{H_3O^+}$ protonates the enolate to give the neutral $\beta$-keto ester product.
• A $\beta$-keto acid decarboxylates on heating by the pattern $\mathrm{RCOCH_2CO_2H} \xrightarrow{\Delta} \mathrm{RCOCH_3} + \mathrm{CO_2}$.

Vocabulary

Claisen condensation

A carbon-carbon bond forming reaction in which ester enolates react with esters to produce $\beta$-keto esters.

Dieckmann condensation

An intramolecular Claisen condensation in which a diester forms a cyclic $\beta$-keto ester.

Enolate

A resonance-stabilized anion formed when a base removes an $\alpha$-hydrogen next to a carbonyl group.

$\alpha$-carbon

The carbon directly next to a carbonyl carbon, often the site where acidic hydrogens are removed.

$\beta$-keto ester

A molecule containing a ketone and an ester separated by one carbon, with the pattern $\mathrm{RCOCH_2COOR'}$.

Decarboxylation

A reaction in which a carboxylic acid derivative loses $\mathrm{CO_2}$, often after heating a $\beta$-keto acid.