العربية
中国
Français
Deutsch
Ελληνική
हिन्दी
Italiano
日本語
Português
Русский
Español1,2-WITTIG REARRANGEMENT
A '1,2-Wittig rearrangement' is a categorization of chemical reactions in Organic chemistry, and consists of a 1,2-rearrangement of an ether with an alkyllithium compound [1] [2].
The intermediate product is an alkoxy lithium salt and the final product an alcohol. When R2 is a good leaving group and electron withdrawing functional group such as a cyanide (CN) group, [3] this group is eliminated and the corresponding ketone is formed.
The reaction mechanism centers on the formation of a free radical pair with lithium migrating from the carbon atom to the oxygen atom. The R radical then recombines with the ketyl ''Wittig Rearrangement of Lithiated Allyl Aryl Ethers: A Mechanistic Study'' Sven Strunk, Manfred Schlosser European Journal of Organic Chemistry Volume '2006', Issue 19 , Pages 4393 - 4397 .
The alkyl group migrates in the order of thermodynamical stability methyl < primary alkyl < secondary alkyl < tertiary alkyl in this is line with the radical mechanism. The radical-ketyl pair is short lived and due to a solvent cage effect some isomerizations take place with retention of configuration.
With certain allyl aryl ethers a competing reaction mechanism takes place . The reaction of ''allyl phenyl ether'' '1' with ''sec-butyllithium'' at -78°C gives the lithiated intermediate '2' which on heating to -25°C only shows the rearranged product '5' but not '4' after trapping the lithium alkoxide with trimethylsilyl chloride. This result rules out a radical-ketyl intermediate '3a' in favor of the Meisenheimer complex '3b'. Additional evidence for this mechanism is provided by the finding that with a para tert-butyl substituent the reaction is retarded.
★ The 1,3-Wittig rearrangement
★ The Smiles rearrangement
1. G. Wittig, L. Löhmann, Ann. 550, 260 ('1942')
2. G. Wittig, Experientia 14, 389 ('1958').
3. ''Preparation of aryl benzyl ketones by [1,2]-Wittig rearrangement'' Alan R. Katritzky, Yuming Zhang, Sandeep K. Singh Arkivoc p. 146-150 '2002' (vii) link
The 1,2-Wittig rearrangement
The intermediate product is an alkoxy lithium salt and the final product an alcohol. When R2 is a good leaving group and electron withdrawing functional group such as a cyanide (CN) group, [3] this group is eliminated and the corresponding ketone is formed.
The 1,2-Wittig rearrangement
| Contents |
| Reaction mechanism |
| See also |
| References |
Reaction mechanism
The reaction mechanism centers on the formation of a free radical pair with lithium migrating from the carbon atom to the oxygen atom. The R radical then recombines with the ketyl ''Wittig Rearrangement of Lithiated Allyl Aryl Ethers: A Mechanistic Study'' Sven Strunk, Manfred Schlosser European Journal of Organic Chemistry Volume '2006', Issue 19 , Pages 4393 - 4397 .
The 1,2-Wittig rearrangement reaction mechanism
The alkyl group migrates in the order of thermodynamical stability methyl < primary alkyl < secondary alkyl < tertiary alkyl in this is line with the radical mechanism. The radical-ketyl pair is short lived and due to a solvent cage effect some isomerizations take place with retention of configuration.
With certain allyl aryl ethers a competing reaction mechanism takes place . The reaction of ''allyl phenyl ether'' '1' with ''sec-butyllithium'' at -78°C gives the lithiated intermediate '2' which on heating to -25°C only shows the rearranged product '5' but not '4' after trapping the lithium alkoxide with trimethylsilyl chloride. This result rules out a radical-ketyl intermediate '3a' in favor of the Meisenheimer complex '3b'. Additional evidence for this mechanism is provided by the finding that with a para tert-butyl substituent the reaction is retarded.
1,2-Wittig rearrangement competing mechanism
See also
★ The 1,3-Wittig rearrangement
★ The Smiles rearrangement
References
1. G. Wittig, L. Löhmann, Ann. 550, 260 ('1942')
2. G. Wittig, Experientia 14, 389 ('1958').
3. ''Preparation of aryl benzyl ketones by [1,2]-Wittig rearrangement'' Alan R. Katritzky, Yuming Zhang, Sandeep K. Singh Arkivoc p. 146-150 '2002' (vii) link
This article provided by Wikipedia. To edit the contents of this article, click here for original source.
psst.. try this: add to faves
