Sign In Forgot Password Register username password If you like us, please share us on social media. The latest UCD Hyperlibrary newsletter is now complete, check it out. ChemWiki BioWiki GeoWiki StatWiki PhysWiki MathWiki SolarWiki Periodic Table of the Elements Reference Tables Physical Constants Units & Conversions Lab Techniques ChemWiki: The Dynamic Chemistry E-textbook > Organic Chemistry > Reactivity of Alpha Hydrogens > Claisen Reactions Because esters can contain α hydrogens they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. In a fashion similar to the aldol, one ester acts as a nucleophile while a second ester acts as the electrophile. During the reaction a new carbon-carbon bond is formed. The product is a β-keto ester. A major difference with the aldol reaction is the fact that hydroxide cannot be used as a base because it could possibly react with the ester. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. ClaisenCondensation Basic reaction Going from reactants to products simply Example 1: Claisen Condensation ClaisenCondensationM echanism 1) Enolate formation Claisen Reactions - Chemwiki http://chemwiki.ucdavis.edu/Organic_Chemistry/Reactivity_of_Alpha... 1 of 2 30-Apr-15 4:21 PM

Claisen Reactions - Chemwiki

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details of claisen reaction required for celoxib synthesis.

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ChemWiki BioWiki GeoWiki StatWiki PhysWiki MathWiki SolarWiki

Periodic Table of the Elements Reference Tables Physical Constants Units & Conversions Lab Techniques

ChemWiki: The Dynamic Chemistry E-textbook > Organic Chemistry > Reactivity of Alpha Hydrogens > Claisen Reactions

Because esters can contain α hydrogens they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. In afashion similar to the aldol, one ester acts as a nucleophile while a second ester acts as the electrophile. During the reaction a new carbon-carbon bondis formed. The product is a β-keto ester. A major difference with the aldol reaction is the fact that hydroxide cannot be used as a base because itcould possibly react with the ester. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification sideproducts.

Claisen CondensationBasic reaction

Going from reactants to products simply

Example 1: Claisen Condensation

Claisen Condensation M echanism1) Enolate formation

Claisen Reactions - Chemwiki http://chemwiki.ucdavis.edu/Organic_Chemistry/Reactivity_of_Alpha...

1 of 2 30-Apr-15 4:21 PM

2) Nucleophilic attack

3) Removal of leaving group

Dieckm ann CondensationA diester can undergo an intramolecular reaction called a Dieckmann condensation.

Example 2: Dieckman Condensation

Crossed Claisen CondensationClaisen condensations between different ester reactants are called Crossed Claisen reactions. Crossed Claisen reactions in which both reactants canserve as donors and acceptors generally give complex mixtures. Because of this most Crossed Claisen reactions are usually not performed unless onereactant has no alpha hydrogens.

Example 3: Crossed Claisen Condensation

ContributorsProf. Steven Farmer (Sonoma State University)

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Claisen Reactions - Chemwiki http://chemwiki.ucdavis.edu/Organic_Chemistry/Reactivity_of_Alpha...

2 of 2 30-Apr-15 4:21 PM