Claisen rearrangement

Some Concepts Of Claisen Rearrangement

1. 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 REARRANGEM ENT .

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

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