Homologation reaction

A homologation reaction, also known as homologization, is any chemical reaction that effects an overall increase of the carbon skeleton of a saturated reactant molecule.[1] The reactants undergo a homologation converting them into the next member of the homologous series. For example the reaction of aldehydes and ketones with diazomethane or methoxymethylenetriphenylphosphine effectively inserts a methylene (-CH2-) unit in the hydrocarbon chain and the reaction product is the next homologue.

Examples of homologation reactions include:

* Seyferth-Gilbert homologation
* Displacement of a halide by a cyanide group, which can be reduced to an amine
* Kiliani-Fischer synthesis, where an aldose molecule is elongated through a three-step process consisting of:
1. Nucleophillic addition of cyanide to the carbonyl to form a cyanohydrin
2. Hydrolysis to form a lactone
3. Reduction to form the homologous aldose
* Wittig reaction of an aldehyde with methoxymethylenetriphenylphosphine, which produces a homologous aldehyde.
* Arndt-Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue (ie. contains one additional carbon atom)
* Kowalski ester homologation, an alternative to the Arndt-Eistert synthesis. Has been used to convert β-amino esters from α-amino esters through an ynolate intermediate.[2]

Some reactions increase the chain length by more than one unit. For example, the following are considered two-carbon homologation reactions:

* Nucleophilic addition to ethylene oxide, resulting in a ring-opening and producing a primary alcohol with two extra carbons.
* Malonic ester synthesis, which produces a carboxylic acid with two extra carbons.

## See also[edit | edit source]

* Homologous series

## References[edit | edit source]

1. ↑ Encyclopedia of Inorganic Chemistry doi:10.1002/0470862106.id396
2. ↑ D. Gray, C. Concellon and T. Gallagher (2004). "Kowalski Ester Homologation. Application to the Synthesis of β-Amino Esters". J. Org. Chem. 69 (14): 4849–4851. doi:10.1021/jo049562h.

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