Hydroalkylation

Hydroalkylation is a class of hydrofunctionalization reactions in which an alkyl group and a hydrogen atom are added across a multiple bond, typically an alkene or an alkyne, to give an alkyl-substituted saturated product. The process forms a new carbon–carbon bond and a C–H bond in a single operation, enabling direct construction of complex alkanes from unsaturated substrates.

Most commonly, hydroalkylation proceeds via a metal-catalyzed hydrometallation step in which a metal hydride adds to the unsaturated partner to generate a metal–alkyl intermediate, followed by cross-coupling with an alkyl source. Alternative radical or photoredox pathways can generate the alkyl fragment, enabling hydroalkylation with alkyl halides, redox-active esters, or organoboron reagents. Nickel- and copper-based catalysts are especially common; palladium and iron catalysts have also been used. Photoredox-enabled methods expand the scope to unactivated alkyl electrophiles and allow milder conditions.

Substrates and selectivity: terminal alkenes often give linear or branched products depending on the catalyst; internal alkenes are less reactive and often give mixtures. Regioselectivity can be tuned toward Markovnikov or anti-Markovnikov products, and stereoselectivity can be achieved in some cases. Functional groups tolerant of hydroalkylation conditions typically include esters, amides, and nitriles, with appropriate catalyst and conditions.

Applications and limitations: hydroalkylation provides a direct route to dialkylated alkane motifs, supporting rapid assembly of complex molecules and late-stage functionalization in organic synthesis. Limitations include competing side reactions such as beta-hydride elimination, substrate scope limitations for certain alkyl sources, and sensitivity to reagent reactivity and conditions.