Aldol reaction PDF
Preview Aldol reaction
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
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