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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Presentation Transcript
slide2

Formation of carbon-carbon bond

1.

Free radical carbon

2.

Charged or polar carbon

slide3

shape of the carbanion

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

conjugated with other

double bond

slide4

Formation of carbanion

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

slide5
Activating group for the neighboring H
  • NO2 > COR > CN > CO2R
  • Strength order of some commonly used bases:
slide6

Factors influencing the stability of carbanions

  • 1. Conjugation
  • 2. Induction
  • 3. Hybridization style
  • 4. Aromaticity
  • The reactions of carbanions
  • 1. With carbonyl-containing compounds
  • 2. With alkyl halides
ketone
Ketone

Rate-determining step

slide9

Some applications of aldol condensation

One aldehyde containing no active hydrogen:

Formaldehyde is the most reactive among the aldehydes

slide18

g) The Knoevenagel Reaction

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.

slide22

b) The Dieckmann Condensation

Intramolecular Claisen condensation

Forming five- or six-membered ring

slide23

c) The Thorpe Reaction

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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