Carbanions and base catalyzed formation of carbon carbon bonds
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Carbanions and Base-catalyzed Formation of Carbon-Carbon Bonds. Formation of carbon-carbon bond. 1. Free radical carbon. 2. Charged or polar carbon. shape of the carbanion. I. Formation and related principle of carbanion ( concepts and mechanisms) Review. conjugated with other

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Formation of carbon-carbon bond Bonds

1.

Free radical carbon

2.

Charged or polar carbon


shape of the carbanion Bonds

  • I. Formation and related principle of carbanion ( concepts and mechanisms)

  • Review

conjugated with other

double bond


Formation of carbanion Bonds

1.exchanging of organometallic compound and H

2.exchanging of organometallic compound and halides

3.reduction of halides with metal

4.abstraction of activating H with base




Ii condensations of carbanions with aldehydes and ketones
II. BondsCondensations of Carbanions with Aldehydes and Ketones

  • a) The Aldol Condensation

Mechanism


Ketone
Ketone Bonds

Rate-determining step


Some applications of aldol condensation Bonds

One aldehyde containing no active hydrogen:

Formaldehyde is the most reactive among the aldehydes






e) The Darzens Reaction Bonds

The net result:



Ketone do not undergo the reaction with malonic acid or its esters,

but do so with cyanoacetic acid and its ester.( with more highly

active a-hydrogen.


Iii condensations of carbanion with esters
III.Condensations of Carbanion with Esters Bonds

  • a) The Claisen Condensation



Intramolecular Claisen condensation

Forming five- or six-membered ring


For the syntheses of various cyclic compounds

In a very dilute ether solution

Using hindered and less nucleophilic base like LiNEtPh


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