carbonylcompounds )depa.fquim.unam.mx/amyd/archivero/reaccionesencalfa... · 2013. 4. 23. ·...
TRANSCRIPT
Carbonyl Compounds
Reac%ons at the α-‐Carbon
Reac%ons at the α-‐Carbon
Acidity of α-‐Hydrogens
resonance contributors
Keto–Enol Tautomerism
The pKa Values of Some Carbon Acids
resonance contributors for the 2,4-‐pentanedione anion
Keto–Enol Tautomerism
base-‐catalyzed keto–enol interconversion
acid-‐catalyzed keto–enol interconversion
How Enols and Enolate Ions React?
acid-‐catalyzed α-‐subs%tu%on reac%on
base-‐catalyzed α-‐subs%tu%on reac%on
resonance contributors of an enolate ion
An ambident nucleophile is a nucleophile with two nucleophilic sites (“two teeth”).
Halogena%on of the α-‐Carbon of Aldehydes and Ketones
Under acidic condi%ons, one α-‐hydrogen is subs%tuted for a halogen.
acid-‐catalyzed halogena%on
Base-‐Promoted Halogena%on
Under basic condi%ons, all the α-‐hydrogens are subs%tuted for halogens.
base-‐promoted halogena%on
the haloform reac%on
Using LDA to Form an Enolate
LDA is a strong base but a poor nucleophile!
LDA is easily prepared by adding butyllithium to diisopropylamine (DIA) in THF -‐78 °C.
Alkyla%on of the α-‐Carbon of Carbonyl Compounds
The rela%ve amounts of the two products depend on the reac%on condi%ons.
Alkyla%on and Acyla%on of the α-‐Carbon via an Enamine Intermediate
Alkyla%on of the α-‐Carbon: The Michael Reac%on
mechanism of the Michael reac%on
mechanism of the Stork enamine reac%on
Alquilación de enolatos
La reacción aldólica
aldol addi%ons
mechanism for the aldol addi%on
Ketones are less suscep%ble than aldehydes to a\ack by nucleophiles so aldol addi3ons occur more slowly with ketones.
Dehydra%on of Aldol Addi%on Products
Forma%on of α,β-‐Unsaturated Aldehydes and Ketones
Reacción aldólica cruzada
The Mixed Aldol Addi%on
The Claisen Condensa%on
When two molecules of an ester undergo a condensa%on reac%on, the reac%on is called a Claisen condensa9on.
mechanism for the Claisen condensa%on
The Claisen condensa%on is a subs%tu%on reac%on, whereas the aldol addi%on is an addi%on reac%on.
The Mixed Claisen Condensa%on
condensa%on of a ketone and an ester
Intramolecular Claisen Condensa%ons
The Robinson Annula%on