Aldol reaction

39 Pages·2017·1.74 MB·English

ORGANIC SYNTHESIS
CHE 416
BY
ADEWUYI Adewale
Chemical Sciences
Redeemer’s University
This work is licensed under a Creative Commons Attribution-ShareAlike4.0 International License.
1: Aldol reaction
• Aldol reaction is a means of forming carbon–
carbon bonds in organic chemistry. It unites two
relatively simple molecules into a more complex
one.
• Aldol' is an abbreviation of aldehyde and alcohol.
When the enolate of an aldehyde or a ketone
reacts at the α-carbon with the carbonyl of
another molecule under basic or acidic conditions
to obtain β-hydroxy aldehyde or ketone, this
reaction is called Aldol Reaction.
• Increased complexity arises because up to two
new stereogenic centers are formed (modern
methods are being developed with high yield).
Hypothetical example
Mechanism of the Aldol Addition
Aldol Condensation
In some cases, the adducts obtained from the Aldol Addition can easily be converted (in situ)
to α,β-unsaturated carbonyl compounds, either thermally or under acidic or basic catalysis.
The formation of the conjugated system is the driving force for this spontaneous dehydration.
Under a variety of protocols, the condensation product can be obtained directly without
isolation of the aldol.
Mechanism of the Aldol Condensation
2: Alder-Ene Reaction/Ene reaction
The ene reaction (also known as the Alder-ene reaction) is a chemical reaction between
an alkene with an allylic hydrogen(the ene) and a compound containing a multiple bond
(the enophile), in order to form a new σ-bond with migration of the ene double bond
and 1,5 hydrogen shift. The product is a substituted alkene with the double bond shifted
to the allylic position
Mechanism of the Alder-Ene Reaction
3: Azo Coupling
Azo coupling is the most widely used industrial reaction in the production of dyes, lakes
and pigments. Aromatic diazonium ions acts as electrophiles in coupling reactions with
activated aromatics such as anilines or phenols. The substitution normally occurs at the
para position, except when this position is already occupied, in which case ortho position
is favoured. The pH of solution is quite important; it must be mildly acidic or neutral, since
no reaction takes place if the pH is too low.
Mechanism of Azo Coupling
4: Beckmann Rearrangement
The Beckmann rearrangement is an acid-catalyzed
rearrangement of an oxime to an amide. Cyclic oximes
yield lactams.
Mechanism of the Beckmann Rearrangement
5: Acetoacetic-Ester Condensation/Claisen Condensation
The Claisen condensation is a carbon–carbon bond forming reaction that occurs between
two esters or one ester and another carbonyl compound in the presence of a strong base,
resulting in a β-keto ester or a β-diketone
Reaction mechanism