Enolates Michael addition reaction

The stereochemical outcome of the Michael addition reaction with substituted starting materials depends on the geometry of the a ,/3-unsaturated carbonyl compound as well as the enolate geometry a stereoselective synthesis is possible. " Diastereoselectivity can be achieved if both reactants contain a stereogenic center. The relations are similar to the aldol reaction, and for... 

An intramolecular version of enolate Michael addition to enantiomerically pure vinylic sulfoxides is represented by reaction of a cyclopentenone sulfoxide with dichloroketene (Scheme 5)90 this type of additive Pummerer rearrangement has been developed by Marino and coworkers91 into a highly effective way of constructing variously substituted lactones in very high enantiomeric purity (equation 43). 

Main group organometallic polymerization catalysts, particularly of groups 1 and 2, generally operate via anionic mechanisms, but the similarities with truly coordinative initiators justify their inclusion here. Both anionic and coordinative polymerization mechanisms are believed to involve enolate active sites, (Scheme 6), with the propagation step akin to a 1,4-Michael addition reaction. 

Oare, D. A., Stereochemistry of the Base-Promoted Michael Addition Reaction, 19, 227 Acyclic Stereocontrol in Michael Addition Reactions of Enamines and Enol Ethers, 20, 87 Okamoto, Yoshio, Optically Active Polymers with Chiral Recognition Ability, 24, 157. 

Acyclic Steieocontrol in Michael Addition Reaction of Enamines and Enol... 

Michael Addition Reactions of Enamines and Enol Ethers, Acyclic Stereocontrol... 

A Michael addition reaction of BusSnLi to enones can be used for the generation of lithium enolates of / -tributylstannyl ketones. The two examples shown in Scheme 13 employed such a route for the generation of ketone ,/i-dianions13. 

C. H. Heathcock, in Asymmetric Synthesis (Ed. J. P. Morrison), Vol. 3, Academic Press, New York, 1984, p. Ill for a review of stereocontrol in Michael addition reactions of enamines and enol ethers, see Reference 27. 

The mechanism of the Michael addition reaction using ester 3.3 and mesityl oxide is shown in Scheme 3.13. The enolate A derived from the malonic ester (3.3) attacks the (3-carbon... 

Enamines undergo the Michael addition reaction to give the least substituted product in contrast to the highly substituted product obtained from enolate derived from unsymmet-rical ketone by Sodium ethoxide (NaOEt) in ethanol (EtOH). 

Recently, Shchepin and coworkers described Michael addition reactions with zinc ketone enolates (144) for the preparation of chroman-2-one derivatives 146. The enolates were generated in situ from a-bromo ketones 143 by addition of excess zinc (equation 40), and subsequent conjugate addition to a, S-unsaturated ketones (145) (equation 40 ) provided chroman-2-ones (146a, b) in yields up to 82% . 

An interesting feature of Michael addition reactions is that Michael acceptors with a leaving group (mostly halides) in y-position can be used for the synthesis of cyclopropanes. The so-called Michael-initiated ring closure reaction (MIRC reaction) starts with an addition of a nucleophile to the a,/3-unsaturated carbonyl, and afterwards the intermediate enolate displaces the leaving group to give the desired cyclopropanes. ... 

The enantioselective Michael addition reaction of tin(II) enolates to a,p-unsaturated ketones is also successfully achieved by employing the chiral diamine 1 to yield the desirable optically active adduct (eq 10). ... 

Murahashi and Naota studied the reaction mechanism of cyclopentadienyl ruthenium enolate complex-catalyzed aldol and Michael addition reactions [80-82]. This mechanistic study revealed that the cone angle of the tertiary phosphine ligands largely affects the stability of C- and N-bound complexes [80, 82], Thus, ligation of bulky phosphine ligand would favor the N -bound complexes [80]... 

Cuprates react only very slowly with Me3SiCl so it can be present during the Michael addition reaction, enhancing the rate of the reaction and the proportion of 1,4-addition, and trapping the enolate product as the silyl enol ether.18 22 Thus the troublesome enone 42 gives good yields of... 

Conjugate addition of a nucleophile to an activated olefin is generally referred to as a Michael addition reaction (1). Of particular interest is the addition of delocalized carbanions to unsaturated acceptors, a process resulting in the construction of a carbon-carbon bond, often stereoselectively (2). However, the addition of metal enolates to unsaturated acceptors is not completely general and two major modifications have been developed wherein covalently bound enolate equivalents are added to unsaturated acceptors. 

Enamine and Lewis-acid-catalyzed Michael additions provide a useful complement to the enolate Michael addition. These variants allow for the reaction to be carried out under nearly neutral or formally acidic conditions. In terms of the stereochemistry, the enolate Michael addition appears at this point to be more versatile in that both stereoisomers are often obtainable from a given set of substrates. However, in particular cases, the enamine or the... 

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