Química Orgánica 2 · Enoles, enolatos y reacciones en alfa
2-Hydroxy-6-methylcyclohexan-1-one by Rubottom oxidation
Condiciones: mCPBA, CH2Cl2; then H3O⁺
Dibuja este problema tú mismo
Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 7 pasos escritos
mCPBA epoxidizes the electron-rich alkene
The silyloxy group makes the C=C very electron-rich. In one concerted step the π bond attacks the terminal peroxy oxygen, the O–O bond breaks, and the peracid proton moves to its carbonyl oxygen.
Las flechas curvas
- The alkene π electrons attack the outer peroxy oxygen.
- The weak O–O bond breaks toward the carbonyl carbon, forming a C=O.
- The original C=O π electrons pick up the peracid proton.
- The O–H electrons form the second C–O bond of the epoxide.
Acid protonates the epoxide oxygen
In the acidic workup hydronium protonates the epoxide oxygen, turning it into a good leaving group.
Las flechas curvas
- The epoxide oxygen lone pair takes the proton.
- The O–H electrons stay on water.
The silyloxy oxygen opens the epoxide
The silyloxy lone pair pushes into the ring carbon it is attached to, breaking that C–O bond. The cation formed is an oxocarbenium ion, and the other carbon keeps the new OH.
Las flechas curvas
- The silyloxy lone pair forms a C=O⁺ π bond.
- The C–O bond of the protonated epoxide breaks onto oxygen.
Why the oxygen ends up on that carbon
The epoxide oxygen is delivered to the carbon that was the β-carbon of the enol ether.
Water removes the silyl group
Water attacks silicon, and the Si–O bond breaks onto the oxocarbenium oxygen, releasing the neutral ketone.
Las flechas curvas
- A water lone pair bonds to silicon.
- The Si–O electrons move onto the carbonyl oxygen.
Water deprotonates the silyloxonium
A second water removes the proton from the positive oxygen on silicon, giving trimethylsilanol and regenerating hydronium.
Las flechas curvas
- A water lone pair takes the proton.
- The O–H electrons stay on oxygen.
2-Hydroxy-6-methylcyclohexan-1-one
The α-carbon of the former enol ether now carries an OH and the silyloxy carbon is a ketone. The silyl group leaves as trimethylsilanol and mCPBA becomes 3-chlorobenzoic acid.
Qué vas a practicar
Draw epoxidation of the silyl enol ether by mCPBA, acid opening of the siloxy epoxide and removal of the silyl group to give the α-hydroxy ketone.
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