Conjugate additions enones

A proposed simplified mechanism for the conjugate addition/aldol cyclization, as depicted in Scheme 2.25, is based on detailed mechanistic studies performed on related Rh-catalyzed enone conjugate additions [45]. A model accounting for the observed relative stereochemistry invokes the intermediacy of a (Z)-enolate and a Zimmerman-Traxler-type transition state as shown in 2-110 to give 2-111. 

Michael reaction with exocycHc ,(S-enones Conjugate addition of secondary amines to a,/ -enones proceeds readily unless the enonc is cxocyclic. in "Such a case the reaction is very slow unless alumina is added as catalyst. Thus the reaction of 1 and diethylamine in the presence of alumina proceeds in 2 hours to give 2 quantitatively. 

Magnus, P. Lacour, J. Evans, P. A. Rigollier, P. Tobler, H. Applications of the /i-azidonation reaction to organic synthesis. a,/i-Enones, conjugate addition, and /-lactam annulation. 

Alkyl halides (particularly bromides) undergo oxidative addition with activated copper powder, prepared from Cu(I) salts with lithium naphthalenide, to give alkylcopper species10. The alkyl halides may be functionalized with ester, nitrile and chloro functions ketone and epoxide functions may also be tolerated in some cases11. The resulting alkylcopper species have been shown to react efficiently with acid chlorides, enones (conjugate addition) and (less efficiently) with primary alkyl iodides and allylic and benzylic bromides (equations 5 and 6). If a suitable ring size can be made, intramolecular reactions with epoxides and ketones are realized. 

The reaction with EtAlCb is a Lewis-acid-catalysed conjugate addition of the allyl silane on to the enone. Conjugate addition is preferred because the nucleophile (allyl silane) is tethered to the electrophile (enone) and the five-membered ring is easier to form than the alternative seven-membered ring. 

Another approach for annulation at the less substituted carbon is to first form the kinetic enolate using one of several methods (e.g., LDA, Birch reduction of an enone, conjugate addition of an organocuprate to an enone) followed by reaction with MVK and cyclization. 

Reaction with Cyclic Enones. Conjugate addition of azide ion to cyclic enones in water using sodium azide in the presence of Lewis base resulted in the formation of 8-azido carbonyl compounds (eq 55). The Schmidt reaction of benzopyranones with sodium azide led to pyrano[3,2-b]azepines in reasonable yields (eq 56). 

Vinylcyclopropanation of Enones. Conjugate addition of sulfur-stabilized aUyl carbanions to a. -unsaturated ketones produces enolates that cyclize to vinylcyclopropyl ketones upon treatment with nearly one equivalent of (CuOTf)2-C6H6, i.e. 1.9 equivalents of Cu (eq 68). ... 

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