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:

Some reactions increase the chain length by more than one unit. For example, the DeMayo reaction can be considered a two-carbon homologation reaction.

Chain reduction

Likewise the chain length can also be reduced:

Gallagher-Hollander Degradation
Hooker reaction
Mechanistically oxidation causes ring-cleavage at the alkene group, extrusion of carbon dioxide in decarboxylation with subsequent ring-closure.

See also

References

  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. PMID 15230615.
  3. Vincent P. Hollander and T. F. Gallagher PARTIAL SYNTHESIS OF COMPOUNDS RELATED TO ADRENAL CORTICAL HORMONES. VII. DEGRADATION OF THE SIDE CHAIN OF CHOLANIC ACID J. Biol. Chem., Mar 1946; 162: 549 - 554 Link
  4. On the Oxidation of 2-Hydroxy-1,4-naphthoquinone Derivatives with Alkaline Potassium Permanganate Samuel C. Hooker J. Am. Chem. Soc. 1936; 58(7); 1174-1179. doi:10.1021/ja01298a030
  5. On the Oxidation of 2-Hydroxy-1,4-naphthoquinone Derivatives with Alkaline Potassium Permanganate. Part II. Compounds with Unsaturated Side Chains Samuel C. Hooker and Al Steyermark J. Am. Chem. Soc. 1936; 58(7); pp 1179 - 1181; doi:10.1021/ja01298a031
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