Page 704 - Advanced Organic Chemistry Part B - Reactions & Synthesis

680 The 1:1 organocopper reagents can be prepared directly from the halide and highly
reactive copper metal prepared by reducing Cu(I) salts with lithium naphthalenide. 19
CHAPTER 8 This method of preparation is advantageous for organocuprates containing substituents
Reactions Involving that are incompatible with organolithium compounds. For example, nitrophenyl and
Transition Metals
cyanophenyl copper reagents can be prepared in this way, as can alkylcopper reagents
having ester and cyano substituents. 20 Allylic chlorides and acetates can also be
converted to cyanocuprates by reaction with lithium naphthalenide in the presence of
CuCN and LiCl. 21

Li naphthalenide
(CH ) C CHCH Cl [(CH ) C CHCH ] CuCNLi 2
3 2
2 2
3 2
2
CuCN, LiCl
Organocopper reagents can also be prepared from Grignard reagents, which are
generated and used in situ by adding a Cu(I) salt, typically the bromide, iodide, or
cyanide.
8.1.2. Reactions Involving Organocopper Reagents and Intermediates

The most characteristic feature of the organocuprate reagents is that they are

excellent soft nucleophiles, showing greater reactivity in S 2 S 2 , and conjugate
N
N
addition reactions than toward direct addition at carbonyl groups. The most important
reactions of organocuprate reagents are nucleophilic displacements on halides and
sulfonates, epoxide ring opening, conjugate additions to -unsaturated carbonyl
compounds, and additions to alkynes. 22 These reactions are discussed in more detail
in the following sections.

8.1.2.1. S 2 and S 2 Reactions with Halides and Sulfonates. Corey and Posner

N
N
discovered that lithium dimethylcuprate can replace iodine or bromine by methyl in a
wide variety of compounds, including aryl, alkenyl, and alkyl derivatives. This halogen
displacement reaction is more general and gives higher yields than displacements with
Grignard or lithium reagents. 23
I CH 3
) CuLi
+ (CH 3 2
90%
PhCH CHBr + (CH ) CuLi PhCH CHCH 3
3 2
81%

19
G. W. Ebert and R. D. Rieke, J. Org. Chem., 49, 5280 (1984); J. Org. Chem., 53, 4482 (1988);
G. W. Ebert, J. W. Cheasty, S. S. Tehrani, and E. Aouad, Organometallics, 11, 1560 (1992); G. W. Ebert,
D. R. Pfennig, S. D. Suchan, and T. J. Donovan, Jr., Tetrahedron Lett., 34, 2279 (1993).
20 R. M. Wehmeyer and R. D. Rieke, J. Org. Chem., 52, 5056 (1987); T.-C. Wu, R. M. Wehmeyer, and
R. D. Rieke, J. Org. Chem., 52, 5059 (1987); R. M. Wehmeyer and R. D. Rieke, Tetrahedron Lett., 29,
4513 (1988).
21
D. E. Stack, B. T. Dawson, and R. D. Rieke, J. Am. Chem. Soc., 114, 5110 (1992).
22 For reviews of the reactions of organocopper reagents, see G. H. Posner, Org. React., 19, 1 (1972);
G. H. Posner, Org. React., 22, 253 (1975); G. H. Posner, An Introduction to Synthesis Using
Organocopper Reagents, Wiley, New York, 1980; N. Krause and A. Gerold, Angew. Chem. Int. Ed.
Engl., 36, 187 (1997).
23
E. J. Corey and G. H. Posner, J. Am. Chem. Soc., 89, 3911 (1967).