Química Orgânica 2 · Condensação de Claisen e adição conjugada
Acetoacetic ester synthesis — cyclic dialkylation stage
Condições: Ethyl acetoacetate and 1,4-dibromobutane with ethoxide in ethanol. After the first alkylation add a second ethoxide equivalent and follow the dilute intramolecular ring-closure branch. Counterions omitted; no ester cleavage or ketone workup transformation is specified.
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Arraste dos elétrons que se movem até onde eles vão, ou toque em um e depois no outro. Cada seta é verificada; Dica ajuda quando você travar. Não precisa de conta.
O mecanismo, passo a passo
Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
Ler todos os 5 passos escritos
Remove an alpha hydrogen
The first base equivalent generates the active-methylene enolate. The two carbonyl groups remain intact.
Nota: The two drawn alpha hydrogens are equivalent.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Build the specified carbon bond
One end of the dihalide is attached. The other C–Br bond and the remaining hydrogen between the two carbonyls are both retained for ring formation.
Nota: The two ends of the starting dihalide are equivalent. After one end attaches, the other can close the ring.
As setas curvas
- The carbon-centered enolate supplies the new sigma bond.
- The leaving group takes the carbon–halogen bond pair in the same SN2 event.
Remove an alpha hydrogen
The second ethoxide equivalent is now added. It removes the remaining active-methylene hydrogen; the first ethanol and bromide remain present.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Build the specified carbon bond
Intramolecular displacement closes a five-membered ring containing the carbon between the carbonyls and all four tether carbons. No hydrogen moves during this final SN2 step.
As setas curvas
- The carbon-centered enolate supplies the new sigma bond.
- The leaving group takes the carbon–halogen bond pair in the same SN2 event.
Products
The active carbon now bonds to both ends of the four-carbon tether, giving a five-membered ring with ester and acetyl substituents on the same carbon. Two ethanol molecules and two bromides account for both base equivalents and both original alpha hydrogens.
O que você vai praticar
Link intermolecular alkylation to a second deprotonation and five-membered intramolecular SN2 ring closure.
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