Conjugate addition reactions of organocopper reagents

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

G. H. Posner, Conjugate Addition Reactions of Organocopper Reagents, in W. G. Dauben, Ed., Organic Reactions, Vol. 19, Chap. 1, John Wiley Sons, New York, 1972 M. J. Chapdelaine and M. Hulce, Tandem Vicinal Difunctionalization 0-Addition to a,/3-Unsaturated Carbonyl Substrates Followed by cx-Functionalization, in L. A. Paquette, ed., Organic Reactions, Vol. 38, Chap. 

G. H. Posner, Conjugate Addition Reactions of Organocopper Reagents, Org. React. 1972, 19, 1-114. 

Cot gate addition. Conjugate addition reactions of organocopper reagents have been reviewed by Posner. ... 

Synthesis of Chiral Auxiliaries. Their availability and crystalline nature has made camphor derivatives the precursors of choice for the design and synthesis of chiral auxiliaries. 10-Camphorsulfonyl chloride is the starting material for the synthesis of chiral auxiliaries (9)-(12) (eq 2). Sulfonamides (9) and (10) have been used as chiral auxiliaries in a number of reactions, e.g. the Lewis acid-catalyzed Diels-Alder reaction, the [3 + 2] cycloaddition of a nitrile oxide to an acrylate, and the stereoselective conjugate addition reaction of organocopper reagents to ci ,)3-unsaturated esters. ... 

Nakamura, E. (1994) MesSiCl-acceJerated conjugate addition reactions of organocopper reagents, in Organocopper Reagents, A Practical Approach, Chap. 5, (ed. 

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. 

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. 

Review Taylor has reviewed the conjugate addition-enolate trapping reactions of organocopper reagents, in particular of lithium dialkylcuprates (131 references). 

Table 5.12 1,4-Conjugate addition reactions of anion-based organocopper reagents with 2

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. 

As in the case of addition reactions of carbon nucleophiles to activated dienes (Section HA), organocopper compounds are the reagents of choice for regio- and stereoselective Michael additions to acceptor-substituted enynes. Substrates bearing an acceptor-substituted triple bond besides one or more conjugated double bonds react with organocuprates under 1,4-addition exclusively (equation 51)138-140 1,6-addition reactions which would provide allenes after electrophilic capture were not observed (cf. Section IV). 

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