Oxidative alkene cleavage
Lemieux-Johnson oxidation
How the Lemieux-Johnson oxidation works, in 3 steps. Each step shows the structures and the curved arrows that move the electrons.
In short. A 3-step mechanism. Typical reagents: Alkene, OsO₄ (cat., 1–5 mol%), NaIO₄ (≥ 4 equiv.), 2,6-lutidine (optional). Conditions: Dioxane/H₂O or THF/H₂O, 25 °C. Bonds formed: two C=O; IO₃⁻; bonds broken: C=C (σ and π); C–C of the diol. Stereochemistry: Alkene geometry lost; α-stereocentres retained. Rate and selectivity: Osmylation is fast; NaIO₄ turns over Os(VI) → Os(VIII).
At a glance
Step 1: OsO₄ adds across the alkene
OsO₄ adds across the alkene in a concerted [3+2] cycloaddition, giving a cyclic osmate ester, the same first step as Upjohn dihydroxylation.
Step 2: Diol, then periodate ester
Hydrolysis gives a syn-1,2-diol and reduced osmium(VI). NaIO₄ then does two jobs at once: it cleaves the diol through a cyclic periodate ester, and it reoxidizes the osmium back to OsO₄, so only a catalytic amount of the toxic metal is needed.
Step 3: C–C cleavage to two carbonyls
The C–C bond breaks, giving two carbonyl compounds: an aldehyde or ketone from each former alkene carbon. Unlike ozonolysis the reaction runs at room temperature with no ozone generator or explosive ozonide, which is why it is a convenient alternative.
Abbreviations and terms
- THF
- Tetrahydrofuran. Cyclic ether solvent; its oxygen lone pairs solvate Li⁺/Mg²⁺ so organometallics stay dissolved and reactive.
- OsO4
- Osmium tetroxide. Adds syn across alkenes to give diols (via a cyclic osmate ester).
How it compares with related reactions
| Lemieux-Johnson oxidation | KMnO₄ oxidation of an alkene | Ozonolysis | |
|---|---|---|---|
| Reagents | Alkene, OsO₄ (cat., 1–5 mol%), NaIO₄ (≥ 4 equiv.), 2,6-lutidine (optional) | cold dilute KMnO₄, OH⁻ (diol); hot conc. KMnO₄ (cleavage) | 1) O₃ 2) Me₂S or Zn/AcOH (reductive workup) |
| Conditions | Dioxane/H₂O or THF/H₂O, 25 °C | 0–5 °C, basic, vs. heat, acid | CH₂Cl₂ or MeOH, –78 °C |
| Stereochemistry | Alkene geometry lost; α-stereocentres retained | Syn addition (cis diol) in cold conditions | Alkene geometry is lost |
| Rate / selectivity | Osmylation is fast; NaIO₄ turns over Os(VI) → Os(VIII) | Cycloaddition fast; Mn(VII) → Mn(V) → MnO₂ | Fast, even at –78 °C; ozonide is explosive, never isolated |
Test yourself
Try to answer each question before opening it.
Which reagents and conditions are typical for the Lemieux-Johnson oxidation?
Alkene, OsO₄ (cat., 1–5 mol%), NaIO₄ (≥ 4 equiv.), 2,6-lutidine (optional). Conditions: Dioxane/H₂O or THF/H₂O, 25 °C.
Which bonds are formed and which are broken?
Formed: two C=O; IO₃⁻. Broken: C=C (σ and π); C–C of the diol.
What is the stereochemical outcome?
Alkene geometry lost; α-stereocentres retained
What controls the rate or the selectivity?
Osmylation is fast; NaIO₄ turns over Os(VI) → Os(VIII)
Study guides that help with this reaction
- SN1, SN2, E1 or E2? How to decide which mechanism wins
- Nucleophiles, electrophiles and leaving groups: what makes a reaction go