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A Cinchona-derived catalyst can help convert an achiral meso diol into an enantioenriched hydroxyketone by selectively removing one of two equivalent-in-mirror hydrogen atoms. In the 2024 method, light activates the catalyst, and the resulting carbon-centered radical is trapped by an oxidant rather than simply given a hydrogen back. That distinction matters: a related method returns hydrogen and epimerizes the diol instead.
What the Cinchona-derived catalyst does
The method reported by Lam, Dhankhar, Lahdenperä, and Phipps is an example of catalytic enantioselective hydrogen atom abstraction. It starts with a meso diol: a molecule that contains stereogenic centers but is achiral overall because of its symmetry. The two C–H bonds next to an alcohol are enantiotopic, meaning that reacting at one rather than the other can lead to products with different handedness.
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A chiral catalyst derived from Cinchona alkaloids creates a preference between those two hydrogens. After photooxidation, the catalyst’s aminium radical cation abstracts one hydrogen, producing an enantioenriched ketyl radical and establishing stereochemical bias at the neighboring carbon. The authors identify this selective abstraction as the enantiodetermining step. The 2024 JACS paper describes the approach as an oxidative desymmetrization of meso diols.
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How the reaction produces a hydroxyketone
- Photooxidation activates the catalyst. Under blue light, a photocatalyst oxidizes the Cinchona-derived hydrogen-atom-abstraction catalyst.
- The chiral catalyst removes a selected hydrogen. Its aminium radical cation preferentially abstracts one of the enantiotopic C–H hydrogens adjacent to an alcohol.
- An oxidant intercepts the carbon-centered radical. The study reports trapping by DIAD or oxygen.
- Elimination gives the oxidized product. Subsequent in situ elimination yields an enantioenriched hydroxyketone.
This is not a reversible hydrogen-removal-and-replacement cycle. In the oxidation route, the radical’s fate changes the substrate’s functional groups and produces a hydroxyketone.
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What the reported results show
For meso cyclohexane-1,2-diol, a selected condition used epi-NHBoc-DHCN (10 mol%), 4CzIPN (5 mol%), Bu4N·H2PO4 (25 mol%), DIAD, acetonitrile, and blue light. The authors reported 54% yield and 82% enantiomeric excess (ee) at +10 °C; lowering the temperature to −35 °C increased the reported ee to 91%. These are experimental results from the paper’s optimization, not independent replication or evidence of scale-up. See the primary study.
The authors report examples involving cyclic and acyclic meso diols, with some reactions defining as many as four stereocenters in one operation. Substrate scope is not uniform: bulky substrates could show lower enantioselectivity, and the five-membered diol example had lower yield and required telescoped derivatization for isolation. The paper also reports tolerance of functional groups including alkenes, esters, acetals, nitriles, and protected amines.
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How this differs from meso-diol epimerization
A separate 2024 Cinchona-derived hydrogen-abstraction method uses thiol-mediated hydrogen delivery after abstraction. Returning hydrogen can epimerize a meso diol rather than oxidize it into a hydroxyketone; that approach can also be combined with Giese carbon–carbon bond formation. The shared catalyst concept does not make the two reactions interchangeable: the radical’s fate determines whether the outcome is epimerization or oxidation. The Cambridge record for the Science epimerization study describes the hydrogen-return approach.
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- Starting point: both strategies use meso diols, but the desired transformation differs.
- Radical fate: oxidant interception and elimination lead to hydroxyketones; thiol-mediated hydrogen return leads to epimerization.
- Product: oxidation changes the alcohol-bearing framework, while epimerization changes stereochemistry with hydrogen returned.
- Practical scope: the reported oxidation examples vary in yield and selectivity, so results for one substrate should not be generalized to every diol.
The 2024 oxidation study is a laboratory proof of concept, not a consumer procedure. Its catalyst, photocatalyst, oxidant, solvent, and illumination conditions are research inputs, and the reported figures do not establish industrial-scale performance.
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