Organocopper reagents conjugate addition

Organocopper/zirconium reagents. Conjugate addition. Alkylzirci... 

CONJUGATE ADDITION OF ORGANOCOPPER REAGENTS TO a,p-UNSATURATED CARBONYL COMPOUNDS... 

In conclusion, there are only a few examples of conjugate additions with optically active organocopper reagents in which the copper is directly attached to the stereogenic center. There is still room for extensive investigation of this field. 

For the addition of organocopper reagents to alkynes and conjugated dienes, see 15-23. 

Recently, enantiomerically pure vinylic sulfoximines have been shown to undergo effective and highly stereocontrolled conjugate addition of hydrocarbon groups using organocopper reagents . 

Tandem conjugate addition-alkylation has proven to be an efficient means of introducing groups at both a- and (3-positions at enones.307 As with simple conjugate addition, organocopper reagents are particularly important in this application, and they are discussed further in Section 8.1.2.3. 

The mechanism of conjugate addition reactions probably involves an initial complex between the cuprate and enone.51 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species, which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.52 Solvent molecules also affect the reactivity of the complex.53 The mechanism can be outlined as occurring in three steps. 

Scheme 8.2. Conjugate Addition Reactions of Organocopper Reagents...

Scheme 8.3. Tandem Conjugate Addition-Alkylation Using Organocopper Reagents... 

Enantioselective Reactions of Organocopper Reagents. Several methods have been developed for achieving enantioselectivity with organocopper reagents. Chiral auxiliaries can be used for example, oxazolidinone auxiliaries have been utilized in conjugate additions. The outcome of these reactions can be predicted on the basis of steric control of reactant approach, as for other applications of the oxazolidinone auxiliaries. 

Conjugate addition reactions involving organocopper intermediates can be made enantioselective by using chiral ligands.86 Several mixed cuprate reagents containing... 

Feringa, B. L. Naasz, R. Imbos, R. Arnold, L. A. Copper-catalyzed Enantioselective Conjugate Addition Reactions of Organozinc Reagents. In Modem Organocopper Chemistry Krause, N. Ed. Wiley-VCH GmbH Weinheim, 2002 Chapter 7, pp 224—258. 

Conjugate additions to enals and enones.1 ClSi(CH,)3/HMPT markedly accelerates the Cu(I)-catalyzed conjugate addition of Grignard reagents to enals, enones, and unsaturated esters. The conjugate addition of organocopper reagents is also facilitated. 

The conjugate addition of an organocopper reagent to an acceptor-substituted enyne proceeds via 1,6-addition to give an allenic species (Scheme 3.81) [121]. 

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