Organocopper alkylation

The simplest case is the substitution of a halogen at a saturated carbon atom by an alkyl group. Organocopper reagents exhibit strong carbanionic capacity, and do attack ester groups only slowly (D.E. Bergbreiter, 1975). Ketones, however, should be protected. The relative re-... 

Witli tlie reagent PbCu in tlie presence of tlie additives BF and PBu- , ees of up to 9 596 were obtained, wb de values of up to 8 596 were acliievable witli a vinyl copper reagent. Chiral dienic acetals have also been studied tliree regioisomeric products could be obtained in tliis case as tlie result of Su2, Su2, or Su2" attaclt of tlie organocopper reagent [25]. Mixtures were indeed obtained witli alKyl copper reagents, but PbCu-BF resulted in fotniation of only tlie S 2 and Su2" products, witli selectivity for tlie latter fSclieme 8.12). 

Conjugate Addition of Alkyl Groups Organocopper Reactions... 

Organocopper-boron trifluoride (RCu BF3) reacts with allylic alcohols, such as 3-phenyl-2-propenol, 2-butenol, 3-buten-2-ol, 2,4-hexadienol, 3-methyl-2-butenol, to give the y-alkylation... 

This methodology has been extended to the preparation of 3,3-disubstituted cyclopentanones. The yields and the enantiomeric excess of the final product is heavily dependent on the nature of alkyl groups and the organocopper reagent14. 

For use of other organocopper reagents in converting carboxylic acid chlorides to ketones, see G. H. Posner and C. E. Whitten, Tetrahedron Lett., 1815 (1973) G. H. Posner, C. E. Whitten, and P. E. McFarland, J. Amer. Chem. Soc., 94, 5106 (1972). For a recent report on direct and convenient preparation of lithium phenylthio (alkyl)-cuprate reagents, see G H Posner, D J Brunelle, and L. Sinoway, Synthesis, 662 (1974). 

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. 

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

Organocopper chemistry also provides a straightforward synthesis through a special alkylation procedure (Scheme 7-22). An organocopper reagent, generated in situ from equimolar amounts of co-side chain vinyl lithium, Cul, and... 

The organocopper reagents prepared in this way cleave epoxides in high yield with substitution of the alkyl group at the less hindered site. This cleavage has been used to effect intramolecular cyclization (second example). 

Organocopper-Mediated Alkylation of Propargyl Alcohol Derivatives... 

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