Enone. conjugate addition reaction with stability

The 1,4-addition reaction of stabilized allylic carbanions with conjugated enones is normally complicated by the ambident reactivity of the carbanion. Clean 7-selective conjugate addition to cyclic enones, however, has been observed with lithiated allylic sulfoxides, phosphine oxides and phosphonates... 

A series of 1,2-diarylethane-l,2-diamines and/or their metal complexes are effective conjugate addition catalysts involving stabilized donors. In reaction of enamides with alky-lidenemalonic esters a Cu(II) complex of 119 is employed, whereas the strontium complex of the bis(sulfonamide) 120 mediates the addition of malonic esters to enones. ... 

Selenium-stabilized carbanions can be also generated by 1,4-addition of nucleophilic reagents to a-selanyl a,[3-unsaturated carbonyl compounds. The conjugate addition of trialkylsilyllithium compounds to 133, followed by reaction with allyl iodide, afforded the addition products 134 with good m-stereoselectivity (R = Me dr 86 14 R = Ph dr 94 6) (Scheme 34).214 The addition of lithium dialkylcuprates to 2-phenylselanylcycloalk-2-enones has also been used for the synthesis of natural products.215,216... 

There is also a frontier orbital effect that assists conjugate addition over the aldol reaction, You will reeall that the carbonyl carbon is a relatively hard centre, whereas the 3 carbon of an enone is soft, As the nucleophilic enolate becomes more stabilized with extra electron-withdrawing groups, it beeomes increasingly soft and hence more likely to attack the [J carbon,... 

Dehydration sometimes occurs under the conditions in which the aldol addition is carried out, without additional heating. In such cases, the S-hydroxycarbonyl compound is an intermediate and the enone is the final product of the reaction. For example, the 8-hydroxyketone formed from the aldol addition of acetophenone loses water as soon as it is formed, because the double bond formed by loss of water is conjugated not only with the carbonyl group, but also with the benzene ring. Conjugation stabilizes the dehydrated product and therefore makes it relatively easy to form. 

DFT calculations have been used to obtain mechanistic insights into the reaction of sulfur ylides PhHC (S+Me2) with dienals and enones by identifying all key transition states and intermediates along the reaction pathway for the 1,2-, 1,4-, and 1,6-nucleophilic attacks at PhCH=CHCH=CHCH=0 and for the 1,2- and 1,4-attacks at MeCH=CHCOMe. The final outcome of the reaction with both substrates has been found to be decided by the interplay between kinetic and thermodynamic factors. Thus, addition of a semi-stabilized ylide to conjugated carbonyl compounds prefers the 1,4-pathway under thermodynamic conditions, in consonance with the experimental reports. However, the formation of epoxides via a 1,2-addition pathway is equally competitive and could be favoured under kinetic conditions. The 2,3-trans cyclo-propanecarbaldehyde is the major product of the 1,4-addition pathway. The enone also prefers the 1,4-addition. ... 

When a stabilized enolate undergoes a 1,4-conjugate addition with an enone, it is called a Michael reaction. However, many related reactions with analogous mechanisms are also described as Michael additions. Any C=C double bond containing one or more EWGs is referred to as a Michael acceptor and soft nucleophiles that prefer 1,4-addition, including stabilized enolates and organocuprates, are described as Michael donors. ... 

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