Homologation reaction
Chemical reaction which converts between members of a homologous series / From Wikipedia, the free encyclopedia
In organic chemistry, a homologation reaction, also known as homologization, is any chemical reaction that converts the reactant into the next member of the homologous series. A homologous series is a group of compounds that differ by a constant unit, generally a methylene (−CH2−) group. The reactants undergo a homologation when the number of a repeated structural unit in the molecules is increased. The most common homologation reactions increase the number of methylene (−CH2−) units in saturated chain within the molecule.[1] For example, the reaction of aldehydes or ketones with diazomethane or methoxymethylenetriphenylphosphine to give the next homologue in the series.
Examples of homologation reactions include:
- Kiliani-Fischer synthesis, where an aldose molecule is elongated through a three-step process consisting of:
- Nucleophillic addition of cyanide to the carbonyl to form a cyanohydrin
- Hydrolysis to form a lactone
- Reduction to form the homologous aldose
- Wittig reaction of an aldehyde with methoxymethylenetriphenylphosphine, which produces a homologous aldehyde.
- Arndt–Eistert reaction is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue (i.e. 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]
- Seyferth–Gilbert homologation in which an aldehyde is converted to a terminal alkyne and then hydrolyzed back to an aldehyde.
Some reactions increase the chain length by more than one unit. For example, the DeMayo reaction can be considered a two-carbon homologation reaction.