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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Carbanions and base catalyzed formation of carbon carbon bonds

Formation of carbon-carbon bond Bonds

1.

Free radical carbon

2.

Charged or polar carbon


Carbanions and base catalyzed formation of carbon carbon bonds

shape of the carbanion Bonds

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

  • Review

conjugated with other

double bond


Carbanions and base catalyzed formation of carbon carbon bonds

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


Carbanions and base catalyzed formation of carbon carbon bonds


Carbanions and base catalyzed formation of carbon carbon bonds


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


Carbanions and base catalyzed formation of carbon carbon bonds

Some applications of aldol condensation Bonds

One aldehyde containing no active hydrogen:

Formaldehyde is the most reactive among the aldehydes






Carbanions and base catalyzed formation of carbon carbon bonds

e) The Darzens Reaction Bonds

The net result:



Carbanions and base catalyzed formation of carbon carbon bonds

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



Carbanions and base catalyzed formation of carbon carbon bonds

Intramolecular Claisen condensation

Forming five- or six-membered ring


Carbanions and base catalyzed formation of carbon carbon bonds

For the syntheses of various cyclic compounds

In a very dilute ether solution

Using hindered and less nucleophilic base like LiNEtPh