olefination

Olefinination is a class of reactions that form carbon–carbon double bonds (olefins) by transforming carbonyl compounds or related substrates into alkenes. It is a central strategy in organic synthesis for constructing C=C bonds with control over substitution and geometry.

The most widely used olefinination methods arise from carbonyl chemistry. The Wittig reaction couples aldehydes or ketones with phosphoranes (ylides) to give alkenes, with stereochemical outcomes influenced by the nature of the ylide (stabilized versus unstabilized). Horner–Wadsworth–Emmons (HWE) olefinations use phosphonate carbanions and typically provide high E-selectivity, though both E and Z products can be obtained under suitable conditions. Julia olefination and its derivatives (including Kocienski variants) combine carbonyl compounds with sulfones and base to furnish alkenes with strong stereocontrol, often favoring E products and enabling diverse substitution patterns. Peterson olefination employs silylated carbanions and a β-elimination to deliver alkenes with tunable geometry. Tebbe olefination and related methylenation reactions convert carbonyl groups to a methylene unit (–CH2–), effectively inserting a double bond at the carbonyl position to generate vinylidene or exocyclic methylene products.

Stereochemistry is a key consideration in olefininations. The choice of reagent, substrate, and reaction conditions influences E/Z selectivity, and several methods exploit this to access specific alkene geometries. Applications include the modular assembly of natural products, pharmaceuticals, and complex molecular libraries, where reliable formation of alkenes is essential.

Limitations include functional group sensitivity, reagent handling (some methods use air- or moisture-sensitive species), and variations in selectivity that require careful optimization for each substrate.