Hypervalent iodine oxidation
Dess-Martin periodinane oxidation
How the Dess-Martin periodinane 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: Dess–Martin periodinane (DMP), NaHCO₃ optional. Conditions: CH₂Cl₂, 25 °C, 0.5–2 h. Bonds formed: C=O (carbonyl); I(III) species; AcOH; bonds broken: O–H, α C–H, I–OAc. Stereochemistry: No stereo-erosion of α-centres (neutral/buffered). Rate and selectivity: Fast ligand exchange; α-C–H removal is rate-limiting.
At a glance
Step 1: Ligand exchange at I(V)
An alcohol's oxygen displaces one of the hypervalent iodine(V) reagent's acetate ligands, forming a new I–O bond and releasing an equivalent of acetic acid — ligand exchange at a hypervalent center, not the sulfonium activation used in Swern-type oxidations.
Step 2: Acetate removes the α-H
A second acetate, still on iodine, acts as an internal base, removing the alcohol's remaining C–H proton in a five-membered cyclic transition state — geometrically similar to the E1cb-like eliminations of the sulfoxide-based oxidations, just centered on iodine instead of sulfur.
Step 3: Ketone and I(III)
This delivers the carbonyl directly and reduces iodine(V) to iodine(III) — because the reagent is a bench-stable solid needing no low temperatures or foul-smelling sulfides, it's become one of the most widely used mild oxidants in modern synthesis.
Abbreviations and terms
- OAc
- Acetoxy. –OC(=O)CH₃, an acetate group.
- DCM
- Dichloromethane. Common non-polar-ish solvent for reactions that need no nucleophilic or protic solvent.
- AcOH
- Acetic acid. Weak acid and polar protic solvent.
- DMP
- Dess–Martin periodinane. Mild hypervalent-iodine oxidant for alcohols.
- E1cB
- Elimination, unimolecular conjugate base. Deprotonation first to a carbanion, then loss of the leaving group.
How it compares with related reactions
| Dess-Martin periodinane oxidation | Baeyer-Villiger oxidation of a ketone | Collins (Sarett) oxidation | |
|---|---|---|---|
| Reagents | Dess–Martin periodinane (DMP), NaHCO₃ optional | mCPBA or CH₃CO₃H (peracid) | CrO₃·2 pyridine (Collins/Sarett reagent) |
| Conditions | CH₂Cl₂, 25 °C, 0.5–2 h | CH₂Cl₂, 25 °C; cat. acid helps | Anhydrous CH₂Cl₂, 25 °C |
| Stereochemistry | No stereo-erosion of α-centres (neutral/buffered) | Retention at the migrating carbon | Neighbouring stereocentres retained |
| Rate / selectivity | Fast ligand exchange; α-C–H removal is rate-limiting | Migratory aptitude: tert > cyclohexyl ≈ sec > Ph > prim > Me | Alpha C–H cleavage rate-limiting; use 6 equiv reagent |
Test yourself
Try to answer each question before opening it.
Which reagents and conditions are typical for the Dess-Martin periodinane oxidation?
Dess–Martin periodinane (DMP), NaHCO₃ optional. Conditions: CH₂Cl₂, 25 °C, 0.5–2 h.
Which bonds are formed and which are broken?
Formed: C=O (carbonyl); I(III) species; AcOH. Broken: O–H, α C–H, I–OAc.
What is the stereochemical outcome?
No stereo-erosion of α-centres (neutral/buffered)
What controls the rate or the selectivity?
Fast ligand exchange; α-C–H removal is rate-limiting
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