Organometallic — controlled formylation
Bouveault aldehyde synthesis
How the Bouveault aldehyde synthesis 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: n-BuLi or R–MgX (1 equiv.), DMF; then H₃O⁺. Conditions: THF or Et₂O, –78 to 0 °C; aqueous acid workup. Bonds formed: C–C; aldehyde C=O (at workup); bonds broken: C=O π; C–N (at workup). Stereochemistry: None (aldehyde product). Rate and selectivity: Addition fast at low temperature; intermediate stable until workup.
At a glance
Step 1: Organolithium adds to DMF
An organolithium or Grignard reagent attacks DMF's carbonyl carbon — the same nucleophilic acyl substitution mechanism as any amide addition — forming a tetrahedral alkoxide intermediate.
Step 2: Li⁺ chelated; intermediate does not collapse
Just as in Weinreb amide addition, this tetrahedral intermediate is stabilized rather than collapsing immediately, here because the developing alkoxide and the adjacent dimethylamino group can chelate the metal cation, holding the intermediate together until aqueous workup.
Step 3: Aqueous workup releases the aldehyde
Hydrolysis on workup collapses the stabilized intermediate, expelling dimethylamine and revealing the aldehyde — an older, simpler formylation strategy than the Weinreb approach, giving direct access to an aldehyde from any organometallic nucleophile without over-addition to the alcohol.
Abbreviations and terms
- R
- R group. Any carbon substituent (alkyl, aryl…) whose identity does not matter for the mechanism.
- THF
- Tetrahydrofuran. Cyclic ether solvent; its oxygen lone pairs solvate Li⁺/Mg²⁺ so organometallics stay dissolved and reactive.
- Et2O
- Diethyl ether. Low-boiling ether solvent, classic for Grignard reagents.
- DMF
- N,N-Dimethylformamide. Polar aprotic solvent – dissolves ionic nucleophiles but does not H-bond to them, speeding SN2 and SNAr.
- n-BuLi
- n-Butyllithium. Very strong base/nucleophile (pKa of butane ≈ 50); deprotonates alkynes and does lithium–halogen exchange.
How it compares with related reactions
| Bouveault aldehyde synthesis | Grignard addition to acetaldehyde | Grignard addition to an ester (2 equivalents → tertiary alcohol) | |
|---|---|---|---|
| Reagents | n-BuLi or R–MgX (1 equiv.), DMF; then H₃O⁺ | CH₃MgBr in Et₂O or THF; then H₃O⁺ | Ester (methyl benzoate), 2+ equiv. CH₃MgBr, then H₃O⁺ workup |
| Conditions | THF or Et₂O, –78 to 0 °C; aqueous acid workup | Dry ether, 0 °C → 25 °C; strictly anhydrous | Dry Et₂O or THF, 0 °C → 25 °C; then aqueous NH₄Cl or dilute acid |
| Stereochemistry | None (aldehyde product) | Planar C=O: both faces attacked (racemic if new stereocentre) | Product has two identical groups: no stereocentre at carbinol C |
| Rate / selectivity | Addition fast at low temperature; intermediate stable until workup | Fast with aldehydes; RMgX is also a strong base — incompatible with acidic H | Ketone intermediate is more reactive than the ester, so no stop at the ketone |
Test yourself
Try to answer each question before opening it.
Which reagents and conditions are typical for the Bouveault aldehyde synthesis?
n-BuLi or R–MgX (1 equiv.), DMF; then H₃O⁺. Conditions: THF or Et₂O, –78 to 0 °C; aqueous acid workup.
Which bonds are formed and which are broken?
Formed: C–C; aldehyde C=O (at workup). Broken: C=O π; C–N (at workup).
What is the stereochemical outcome?
None (aldehyde product)
What controls the rate or the selectivity?
Addition fast at low temperature; intermediate stable until workup
Study guides that help with this reaction
- Carbonyl chemistry: addition, acyl substitution and enolates
- How to learn reaction mechanisms (without memorising everything)
- How to answer mechanism questions in an exam