Aldehyde conjugate addition reactions

Unimolecular, 373 Unsaturated, 174 Unsaturated aldehyde, conjugate addition reactions of,... 

The mechanism of the cyanide- and thioazolium ion-catalyzed conjugate addition reactions is considered to be analogous to the Lapworth mechanism for the cyanide-catalyzed benzoin condensation. Thus the cyano-stabilized carbanion resulting from deprotonation of the cyanohydrin of the aldehyde is presumed to be the actual Michael donor. After conjugate addition to the activated olefin, cyanide is eliminated to form the product and regenerate the catalyst. 

As with other reactions, silyl esters of phosphorus acids constitute an important and useful category of reagents for conjugate addition reactions. With aldehydes, ketones, and esters, the silyl ester linkage is transferred to the carbonyl oxygen, facilitating the completion of the reaction, generating the free carbonyl or ester upon workup with a protic solvent (Equation 3.25). 

Silyl esters of trivalent phosphorus acids have been used successfully in conjugate addition reactions using acrylates,393 395 nitriles,394 amides,396 397 ketones and aldehydes,398-404 and nitro compounds.387... 

Reactions where NLE have been discovered include Sharpless asymmetric epoxi-dation of allylic alcohols, enantioselective oxidation of sulfides to sulfoxides, Diels-Alder and hetero-Diels-Alder reactions, carbonyl-ene reactions, addition of MesSiCN or organometallics on aldehydes, conjugated additions of organometal-lics on enones, enantioselective hydrogenations, copolymerization, and the Henry reaction. Because of the diversity of the reactions, it is more convenient to classify the examples according to the types of catalyst involved. 

Conjugate addition reactions to enantiomerically pure tolylsulfinyl trifluoro-propene were used recently to prepare a-trifluoromethyl aldehydes [249]. Conjugate adducts were elaborated by Pummerer rearrangement of the sulfoxyl group to install the aldehydic carbonyl (Eq. 83). 

Cuprates formed from organomagnesium reagents are acceptable reagents for the conjugate addition reaction with a, 3-unsaturated aldehydes.81 However, these cuprates are highly dependent upon the choice of copper(I) salt. With CuBr-Me2S, a dramatic increase in 1,4- 1,2-selectivity was reported over... 

Conjugate addition reaction of a mixed dialkylzinc reagent to an unsaturated aldehyde preparation of ethyl (Moxomethyljdecanoate28... 

Two conjugate addition reactions involving a terminal alkyne and an a,p-unsaturated aldehyde lead to 2,3-dihydrothiopyran-4-ones 38 bearing different substituents at the 2- and 6-positions <06TL5095>. 

Acylation of metallated 1-alkynes with dimethylformamide or ethyl chlorofor-mate leads to conjugated acetylenic aldehydes or esters, respectively." These are important substrates for conjugate addition reactions. 

There is a wealth of knowledge about 1,2- and 1,4-conjugate addition reactions [reactions (a) and (b)] for organomagnesium, -zinc, -copper, -aluminium, and -lithium reagents to ketones, aldehydes, and enones These reactions find wide application in organic synthesis. Higher additions (e.g., 1,6-) also occur. ... 

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