organic reaction mechanisms

Theory and Defination :

The Dieckmann condensation is an organic reaction used to form a carbon-carbon bond between two tethered ester groups using an alkoxide base in alcohol to make a cyclic β-keto ester. This reaction is essentially an intramolecular form of the Claisen condensation.
One ester group of the starting material must have an α-hydrogen which is abstracted by the base to form an enolate and alcohol. The enolate then attacks the carbonyl carbon of another ester molecule, an OR group is released to regenerate the base, and the final β-keto ester product is formed. The product in base is then deprotonated again to form another enolate intermediate and acid-workup is required to isolate the final cyclic β-keto ester product.

General Reaction :

Mechanism :

The mechanism is similar to the Claisen Condensation

Examples and Application :

1) Synthesis of Tetronic Acids from Esters

2) Synthesis of 4,4-Disubstituted Cyclohexane β-Keto Esters

Delépine Reaction

Theory and Defination :

The preparation of primary aliphatic amines by acidic hydrolysis of Quaternary amines formed from alkyl halides and urotropine (i.e., hexamethylene tetramine) is known as Delépine reaction. This reaction has an importance in the conversion of alkyl halides into primary amines.

General Reaction :

primary amines (4) is obtained by reaction of a benzyl or alkyl halides

(1) with hexa methylenetetramine

(2) followed by acid hydrolysis of the Quaternary ammonium salt

(3) with aldehyde (5) and ammonium chloride salt .Advantages of this reaction are selective access to the primary anime without side reactions from easily accessible reactants with short reaction times and relatively mild reaction conditions.

Mechanism :

An SN2 reaction leads to the hexa methylene tetramine salt. In chloroform, the starting materials are soluble whereas the products crystallize out. It is usually not possible to purify the salt:

Hexa methylenetetramine is formed in nearly quantitative yield from the condensation of ammonia and formaldehyde.

The compound is rather stable, although dihetero-substituted methylene groups are usually highly reactive. In neutral, aqueous solution, urotropine remains stable even at elevated temperatures. Urotropine decomposes in dilute aqueous acid, and the derived ammonium salts also decompose to form the amine hydrochloride and formaldehyde (and formaldehyde diethylacetal):

During acidic hydrolysis or ethanolysis, semiaminals are formed first; these further decompose to yield formaldehyde or the di-ethylacetal, ammonium salt and the amine hydrochloride:

Examples and Application :

1) preparation of 3-Pyrroline

2) Reactions of alkyl ( halo methyl ) furan carboxylates with hexa methylene tetramine