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Claisen rearrangement

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Apoorv Rastogi

The Claisen rearrangement is a thermal rearrangement reaction discovered by Rainer Ludwig Claisen in which the allyl group of a phenolic allyl ether migrates ortho to the phenol group. Key characteristics of the Claisen rearrangement are the inversion of the migrating allyl carbon and the intramolecular, unimolecular nature of the reaction. The mechanism involves a cyclic transition state that allows for migration to the ortho position, or para if both ortho positions are blocked.

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CLAISEN REARRANGEMENT
Introduction The Claisen Rearrangement is a powerful carbon- carbon bond forming chemical reaction discovered by RAINER LUDWIG CLAISEN. It is the first Sigmatropic Rearrangement
When O-allyl ether of phenol is heated to about 200 degree centigrade in absence of any catalyst, it rearrange to o-allyl phenol.
This THERMAL REARRANGEMENT of PHENOLIC ALLYL ETHERS is called CLAISEN REARRANGEMENT .
It has been observed in this reaction: 1. The allyl group migrates almost invariable to the ortho position unless the ortho position are blocked. 2. There is an inversion of the allyl group during the rearrangement,i.e carbon atom of the allyl group which get attached to the aromatic nucleus is not the one which is attached to the oxygen atom of ether . For example-
3. Rearrangement of mixtures of allyl phenyl ethers do not give cross product, suggesting that the rearrangement is truly intramolecular. 4. When both the ortho positions of phenyl allyl ethers are blocked, the allyl group migrates to para position on CLAISEN REARRANGEMENT. For example-
Mechanism:- The cyclic mechanism, outlined below accounts for the intramolecular rearrangement of allyl ether to ortho allyl phenol.
References 1. Modern Organic Chemistry by M.K. JAIN and S.C. SHARMA 2. Advanced Organic Chemistry by Dr. Jagdamba Singh and Dr. L.D.S Yadav 3. Wikipedia
Claisen rearrangement

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Claisen rearrangement

  • 2. Introduction The Claisen Rearrangement is a powerful carbon- carbon bond forming chemical reaction discovered by RAINER LUDWIG CLAISEN. It is the first Sigmatropic Rearrangement
  • 3. When O-allyl ether of phenol is heated to about 200 degree centigrade in absence of any catalyst, it rearrange to o-allyl phenol.
  • 4. This THERMAL REARRANGEMENT of PHENOLIC ALLYL ETHERS is called CLAISEN REARRANGEMENT .
  • 5. It has been observed in this reaction: 1. The allyl group migrates almost invariable to the ortho position unless the ortho position are blocked. 2. There is an inversion of the allyl group during the rearrangement,i.e carbon atom of the allyl group which get attached to the aromatic nucleus is not the one which is attached to the oxygen atom of ether . For example-
  • 6. 3. Rearrangement of mixtures of allyl phenyl ethers do not give cross product, suggesting that the rearrangement is truly intramolecular. 4. When both the ortho positions of phenyl allyl ethers are blocked, the allyl group migrates to para position on CLAISEN REARRANGEMENT. For example-
  • 7. Mechanism:- The cyclic mechanism, outlined below accounts for the intramolecular rearrangement of allyl ether to ortho allyl phenol.
  • 8. References 1. Modern Organic Chemistry by M.K. JAIN and S.C. SHARMA 2. Advanced Organic Chemistry by Dr. Jagdamba Singh and Dr. L.D.S Yadav 3. Wikipedia