SL - Cross Aldol & Conjugate Addition Flashcards
What is a cross-aldol reaction?
Reaction between 2 different carbonyl compounds
* One must form an electrophile the other must capable of enolization
What 2 conditons must be met for cross aldol to occur?
- One partner must be capable of enolization
- The other partner must be incapable of enolization and be more electrophilic that the other partner
How does the conjugate addition mechanism work?
- Nucleophile attatcks 𝛼,𝛽-unsaturated carbonyl compound at C=C bond (Carboxyl breaks)
- Double bond reformed at adjacent carbon and carboxyl reforms via protonation
- Double bond protonated to form C-C bond
How does the conjugated addition reaction occur with amines?
- The lone pair electrons from nitrogen attacks the conjugate double bond
- We trap the H+ of the N with the enolate (double bond) to form the final compound
Does conjugate addition work with tertiary amines?
Deprotonation cannot occur to produce the final product
Why do alcohols require catalysis to undergo conjugate additions?
They are poor nucleophiles
How does base-catalysed conjugate addition work? (2)
- Deprotonated alcohol attacks C-4 double bond whilst double bond reforms and carbonyl breaks
- Another molecule of the alcohol is deprotonated by the new double bond and the carbonyl reforms
How does acid-catalysed conjugate addition work? (3)
- Carbonyl gets protonated making it a strong enough electrophile to recieve nucleophilic attack
- Alcohol attacks C4, double bond reforms on adjacent carbon, C=O bond breaks
- H+ of the O is trapped by the enol where H+ is eventually regenerated to form the final product
Do thiols require catalysis to undergo conjugate addition?
No- Increased shielding of Sulfurs lone pair (stronger nucleophile)
What are the 3 main steps that occur (at the same time) with most conjugate addition reactions?
- Lone pair of nucleophile attacks (C4) C=C bond
- C=C bond moves to C2-C3 location
- (C2) C=O bond breaks to C-O bond
