Catalytic Isomerization of Allylic Alcohols

Catalytic isomerization of allylic alcohols represents a versatile approach to convert readily available unsaturated alcohols into more synthetically valuable carbonyl compounds. By shifting a hydrogen atom along the carbon framework, allylic alcohols undergo rearrangement to form ketones or aldehydes without the need for stoichiometric oxidants. Transition‐metal complexes—particularly those based on ruthenium, iridium and rhodium—promote a 1,3-hydrogen shift via metal–hydride or π-allyl intermediates. In parallel, organocatalytic protocols exploit strong organic bases to effect proton transfers through ion-pairing and “chain-walking” mechanisms. These catalytic routes not only improve atom economy and operational simplicity, but also enable stereospecific and enantioselective variants, allowing chirality to be transferred from allylic substrates into enolates or carbonyl products. The broad substrate scope, mild conditions and compatibility with further functionalisation have made this field central to the synthesis of fine chemicals, natural products and pharmaceutical intermediates.

Research from Nature Portfolio

Recent studies have demonstrated an umpolung strategy in which iridium(III) catalysts induce a formal 1,3-hydrogen shift in allylic alcohols to generate iridium–enolate intermediates in a stereospecific fashion. These enolates engage electrophiles or undergo intramolecular cyclisations to yield α-functionalised ketones and 3(2H)-furanones as single constitutional isomers, showcasing precise regiocontrol. Detailed mechanistic work, combining experimental and computational evidence, reveals that an iodine(III) reagent promotes nucleophile coupling to the enolate, reversing its conventional reactivity. This approach broadens the scope of catalytic isomerization beyond simple ketone formation and exemplifies how directed enolate chemistry can be conducted in one pot from simple allylic alcohol precursors.

Catalytic Isomerization of Allylic Alcohols publication trend

The graph below shows the total number of articles in catalytic isomerization of allylic alcohols across all publications each year (not limited to Nature Index journals).

Technical terms

Allylic alcohol: An alcohol in which the hydroxyl-bearing carbon is directly adjacent to a carbon–carbon double bond.

Catalytic isomerization: Conversion of one structural isomer into another using a catalyst to lower activation barriers and improve selectivity.

1,3-Hydrogen shift: Intramolecular migration of a hydrogen atom between positions separated by three atoms, often mediated by metal or base catalysts.

Enolate: A resonance-stabilised anion resulting from deprotonation at the α-position of a carbonyl compound, which can undergo further C–C or C–X bond formation.

References

1. Base-Catalyzed Stereospecific Isomerization of Electron-Deficient Allylic Alcohols and Ethers through Ion-Pairing. Journal of the American Chemical Society (2016).
2. How phenyl makes a difference: mechanistic insights into the ruthenium( ii )-catalysed isomerisation of allylic alcohols. Chemical Science (2014).
3. An umpolung strategy to react catalytic enols with nucleophiles. Nature Communications (2019).
4. Base-Catalyzed [1,n]‑Proton Shifts in Conjugated Polyenyl Alcohols and Ethers. ACS Catalysis (2019).