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Activatopm by the cyano-group: III (1) β-alkylation of α,β-unsaturated ketones

✍ Scribed by Alain Debal; The´re`se Cuvigny; Marc Larcheveˆque

Publisher
Elsevier Science
Year
1977
Tongue
French
Weight
137 KB
Volume
18
Category
Article
ISSN
0040-4039

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✦ Synopsis

cx, B-unsaturated ketones are of considerable importance in organic chemistry and a great variety of synthetic methods are available to prepare these compounds ; but some of them are still difficult to obtain. Until now, various procedures have been developed to alkylate an c~, B-unsaturated ketone specifically at the co, c¢' or y position (2, 3, 4), but there are few methods which allow to introduce a substituert at the ~ position (5).

We have previously shown that the cyano groupmay be used as an activating function to synthesize substituted carbonyl compounds and alcohols (1). Because of its electronwithdrawing ability, this function favours the formation of carbanions in cc position and allows to alkylate a molecule in any of its part. We wish to report now that its use provides a good solution to the problem of the B-substitution of ethylenic ketones. This activating group may be introduced by 1-4 addition of cyanide ion to the unsaturated ketone to give a keto-nitrile (6).

Results of previous studies suggested that dianions prepared by removal of t~o hydrogen atoms from this keto-nitrile may be mono-alkylated cc to the nitrile function only.

,,

Thus, it was only necessary to eliminate the nitrile group for isolating a B-substituted ethylenic ketone.

Dianion 3 is obtained from 1 by addition of two equivalents of base. This base ought to be powerful enought to remove a hydrogen in c~ position to the carbonyl function (pKa 'V 18)

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