Homologation reaction

• 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
• 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.
• Seyferth–Gilbert homologation in which an aldehyde is converted to a terminal alkyne and then hydrolyzed back to an aldehyde.

Chain reduction

• In the Gallagher–Hollander degradation pyruvic acid is removed from a linear aliphatic carboxylic acid yielding a new acid with 2 carbon atoms less. The original publication concerns the conversion of bile acid in a series of reactions: acid chloride formation with thionyl chloride, diazoketone formation with diazomethane, chloromethyl ketone formation with hydrochloric acid, organic reduction of chlorine to methylketone, ketone halogenation to 6, elimination reaction with pyridine to enone 7 and finally oxidation with chromium trioxide to bisnorcholanic acid 8.
• In the Hooker reaction an alkyl chain in a certain naphthoquinone is reduced by one methylene unit as carbon dioxide in each potassium permanganate oxidation.