Ketone Formation Gilman Reagent

Acid Chloride Reactions: Ketone formation using Gilmans Reagents

Lithium diorganocuprates (Gilman reagents, R₂CuLi) acylate acid chlorides (RCOCl) to ketones (RCO–R′). The soft cuprate transfers one R group. Ordinary ketones resist further 1,2-addition by the cuprate, allowing them to be isolated; Grignard and organolithium reagents readily add again. Cold, anhydrous ether/THF keeps the cuprate intact; a mild aqueous workup removes copper/lithium salts after collapse.

Highlights: single R transfer (no over-addition), tetrahedral addition intermediate intermediate, chloride expulsion, mild workup that simply strips Cu/Li salts.

Quick Summary

Reagents/conditions: R₂CuLi (1.0–1.5 equiv), acid chloride, Et₂O/THF, −78 → 0 °C, inert; mild NH₄Cl(aq) or dilute acid workup.
Outcome: RCOCl → RCO–R′ (ketone). One R transfers; byproducts RCu + LiCl.
Mechanism: Schematic acyl substitution: R–Cu attack → tetrahedral addition intermediate → collapse, Cl⁻ leaves → ketone; mild workup removes salts.
Selectivity: Softer than RMgX/RLi; ketone survives because the second R does not add.
Exam hook: Contrast with Grignard/organolithium, which over-add to give alcohols.

Mechanism — 3 Steps

Step 1: R from R₂CuLi attacks the acyl carbon; C=O shifts to O⁻ to form a tetrahedral addition intermediate.
Step 1 — R from R₂CuLi attacks the acyl carbon; C=O → O⁻ gives a tetrahedral addition intermediate.
Step 2: Collapse reforms C=O and expels chloride with Cu/Li salts, revealing the ketone framework.
Step 2 — Collapse reforms C=O; Cl⁻ departs with Cu/Li salts, revealing the ketone framework.
Step 3: Mild workup removes Cu/Li salts; the ketone is isolated unchanged.
Step 3 — Mild workup removes Cu/Li salts; the ketone is isolated unchanged.


Mechanistic Checklist

  • One R transfer only; the second R stays on copper (RCu byproduct).
  • Chloride leaves with Cu/Li salts; no protonation of carbonyl needed.
  • Run cold and anhydrous; RMgX/RLi contamination can over-add to the ketone.
  • Ordinary ketones resist further cuprate 1,2-addition; an alpha,beta-unsaturated ketone can instead undergo conjugate addition.


Worked Examples

Reactant

Benzoyl chloride

Reagent

R₂CuLi button

Me₂CuLi; one Me transfers, one stays on Cu.

Me₂CuLi with highlighted Me

Product

Acetophenone

Acetophenone (IUPAC: 1-phenylethan-1-one).

Reactant

Pivaloyl chloride

Reagent

R₂CuLi button

Ph₂CuLi; transfers one phenyl.

Ph₂CuLi with highlighted phenyl

Product

tert-Butyl phenyl ketone

tert-Butyl phenyl ketone (IUPAC: 2-methylpropan-2-yl phenyl ketone).

Reactant

Acetyl chloride

Reagent

R₂CuLi button

n-Bu₂CuLi; transfers one n-Bu.

n-Bu₂CuLi with highlighted n-Bu

Product

2-Hexanone

2-Hexanone (IUPAC: hexan-2-one).



Scope & Limitations

  • Good: Aliphatic, aromatic, and vinyl acid chlorides; symmetric dialkyl or diaryl cuprates; vinyl cuprates.
  • Less suitable: Ordinary esters and amides are generally less reactive; thioesters have their own established cuprate acylation chemistry.
  • Compatibility: Halides, nitriles, ethers often survive; avoid protic solvents that quench the cuprate.
  • Risk: Contaminating RMgX/RLi will over-add to ketones—prepare cuprate cleanly.


Compare dialkylcadmium acylation

Dialkylcadmium reagents, R2Cd, provide another classical acid-chloride-to-ketone route. Ethanoyl chloride and diethylcadmium give butan-2-one: the acid chloride supplies CH3CO and the reagent supplies an ethyl group.

This is an acyl-substitution comparison, not a reason to relabel the copper-containing mechanism above as a cadmium mechanism. Ordinary ketone addition is less favorable than with a Grignard reagent, allowing a ketone endpoint under suitable conditions. Keep the reagent distinction explicit; an acid chloride treated with excess RMgX can instead give a tertiary alcohol.

ethanoyl chloride gives butan-2-one; diethylcadmium; then workup.
Net organic transformation; reagents and product accounting are described above.

Practical Tips

  • Form R₂CuLi from RLi + CuI at −78 °C; allow complete transmetalation before adding acid chloride.
  • Add acid chloride slowly at −78 → 0 °C to maintain selectivity and avoid over-addition.
  • Quench with cold NH₄Cl(aq) or dilute acid; remove Cu/Li salts by filtration/extraction.


Exam-Style Summary

Acid chloride + R₂CuLi → tetrahedral addition intermediate → collapse (Cl⁻ leaves with Cu/Li) → ketone. Only one R transfers; ordinary ketones resist further cuprate 1,2-addition under standard conditions. Cold, anhydrous ether/THF required.



FAQ

Does R₂CuLi over-add to acid chlorides? Ordinary acid-chloride acylation transfers one R and stops before ketone 1,2-addition. An alpha,beta-unsaturated ketone can still undergo conjugate addition.

Why use cold conditions? Keeps the cuprate intact and suppresses side reactions or over-addition by stray RMgX/RLi.

Can cuprates acylate esters? Esters are generally too unreactive toward cuprates; acid chlorides are the preferred electrophile.



Interactive Toolbox

  • Mechanism Solver — open mechanism practice; this exact sequence and reagent toggle have not been verified.
  • Reaction Solver — open reaction practice; automatic outcomes for these exact examples have not been verified.
  • IUPAC Namer — generate names like acetophenone or tert-butyl phenyl ketone.