Methylcopper-Boron Trifluoride Etherate1


[1184-53-8]  · CH3Cu  · Methylcopper-Boron Trifluoride Etherate  · (MW 78.59) (BF3.OEt2)

[109-63-7]  · C4H10BF3O  · Methylcopper-Boron Trifluoride Etherate  · (MW 141.95)

(selective nucleophilic reagent for conjugate additions2 and substitution reactions1)

Preparative Method: prepared by the addition of Boron Trifluoride Etherate to a suspension of Methylcopper in Et2O or THF at -75 °C.2

Handling, Storage, and Precautions: see entries for Boron Trifluoride Etherate and Methylcopper. Use in a fume hood.

Conjugate Additions.

The combination of an alkylcopper with boron trifluoride produces a nucleophilic reagent which is more reactive than the alkylcopper alone and which can exhibit regioselectivity on a par with organocuprate reagents. For example, in each of two syntheses of the sesquiterpene modhephene, RCu/BF3 was used to establish a quaternary center by conjugate addition to a 3-alkyl-2-cyclopentenone moiety (eq 1).3,4 Alkenoates and alkenoic acids are also suitable substrates.2,5 In the development of methodology for asymmetric synthesis, the alkylcopper/BF3 combination was found to be effective in preparing b-substituted carboxylic acids.6 High enantiomeric excesses (94-98%) were obtained by the use of a camphorsulfonamide auxiliary (eq 2).6a

Enhancements of rate and regioselectivity in conjugate additions have also been observed with the combinations of alkylcopper/halosilane7 and alkylcopper/Aluminum Chloride.8

Nucleophilic Substitutions.

Acetals are converted to the corresponding monosubstitution products on treatment with alkylcopper/BF3.9,10 Similarly, orthoformates give acetals in high yield.9 Chiral cyclic acetals undergo this monosubstitution reaction stereoselectively (eq 3), although cuprates with BF3 were found to give better results.10

Allylic halides, ethers, esters, and alcohols suffer regioselective g-attack by alkylcopper/BF3.11 Propargyl chloride and acetate afford 1,2-heptadiene. The stereoselectivity of these substitutions has been less rigorously examined, but appears to be less dramatic than the regioselectivity. The regioselectivity of attack on g-acetoxy-a,b-enoates by alkylcopper/AlCl3 has also been documented.12

Related Reagents.

Methallyllithium; Phenylcopper-Boron Trifluoride Etherate.

1. Yamamoto, Y. AG(E) 1986, 25, 947.
2. Yamamoto, Y.; Yamamoto, S.; Yatagai, H.; Ishihara, Y.; Maruyama, K. JOC 1982, 47, 119.
3. Karpf, M.; Dreiding, A. S. TL 1980, 21, 4569.
4. Schostarez, H.; Paquette, L. A. JACS 1981, 103, 722.
5. Yamamoto, Y.; Maruyama, K. JACS 1978, 100, 3240.
6. (a) Oppolzer, W.; Dudfield, P.; Stevenson, T.; Godel, T. HCA 1985, 68, 212. (b) Oppolzer, W.; Moretti, R.; Bernardinelli, G. TL 1986, 27, 4713.
7. (a) Bergdahl, M.; Lindstedt, E.-L.; Nilsson, M.; Olsson, T. T 1988, 44, 2055. (b) Matsuzawa, S.; Horiguchi, Y.; Nakamura, E.; Kuwajima, I. T 1989, 45, 349. (c) Bergdahl, M.; Lindstedt, E.-L.; Nilsson, M.; Olsson, T. T 1989, 45, 535. (d) Bergdahl, M.; Lindstedt, E.-L.; Olsson, T. JOM 1989, 365, C11.
8. Ibuka, T.; Tabushi, E.; Yasuda, M. CPB 1983, 31, 128.
9. Ghribi, A.; Alexakis, A.; Normant, J. F. TL 1984, 25, 3075.
10. Normant, J. F.; Alexakis, A.; Ghribi, A.; Mangeney, P. T 1989, 45, 507.
11. (a) Yamamoto, Y.; Yamamoto, S.; Yatagai, H.; Maruyama, K. JACS 1980, 102, 2318. (b) Kang, J.; Cho, W.; Lee, W. K. JOC 1984, 49, 1838. (c) Ghribi, A.; Alexakis, A.; Normant, J. F. TL 1984, 25, 3079.
12. Ibuka, T.; Minakata, H. SC 1980, 10, 119.

John N. Haseltine

Georgia Institute of Technology, Atlanta, GA, USA

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