Lithium Bis(1-ethoxyvinyl)cuprate1,2

[123206-02-0]  · C8H14CuLiO2  · Lithium Bis(1-ethoxyvinyl)cuprate  · (MW 212.71)

(vinylcuprate reagent and acyl anion equivalent which undergoes 1,4-addition reactions,3 1,2-addition reactions,4 and substitution reactions3)

Physical Data: homogenous, red solution displaying some temperature sensitivity; dec. estimated between -35 and -25 °C.3

Solubility: sol THF.

Preparative Methods: prepared under an inert atmosphere of argon by the rapid addition of 2 equiv of 1-Ethoxyvinyllithium5 in THF at -78 °C to a suspension of purified Copper(I) Iodide at -78 °C, which is stirred at -30 °C for 1 h to afford a deep red solution.3

Handling, Storage, and Precautions: air- and moisture-sensitive reagent prepared in situ. Use in a fume hood.

Addition Reactions.

Lithium bis(1-ethoxyvinyl)cuprate affords transfer of the 1-ethoxyvinyl ligand, an acyl anion equivalent,6 via conjugate addition to a,b-alkenyl ketones7 (25-91% yield)3 (eqs 1 and 2). This reaction is sensitive to steric hindrance resulting from substitution in the a,b-enone, especially at the b-position, resulting in slow 1,4-addition. Use of excess reagent can sometimes overcome this limitation. The n-propynyl mixed cuprate reagent can be used effectively to give conjugate transfer of the 1-ethoxyvinyl ligand to 2-cyclohexen-1-one (83% yield).3

Employment of Boron Trifluoride Etherate in conjunction with lithium bis(1-ethoxyvinyl)cuprate gives an enhancement of reagent efficiency as well as improved control over the regioselectivity in the reaction, preventing 1,2-addition (eq 3).8

A lithium bis(1-ethoxyvinyl)cyanocuprate reagent can be prepared by the transmetalation of the vinylstannane with lithium dimethylcyanocuprate to give effective conjugate addition of the 1-ethoxyvinyl ligand to an a,b-enone.9 The resulting vinyl ether 1,4-adducts can be readily hydrolyzed under mildly acidic conditions (0.1 N HCl/ether, 0.1 N oxalic acid/MeOH, or SiO2 in wet benzene) to afford 1,4-diketones in 57-95% yield.3

Chemoselective 1,2-addition of lithium bis(1-ethoxyvinyl)cuprate to an aldehyde can be achieved in moderate yield (eq 4).4

Substitution Reactions.

Coupling of lithium bis(1-ethoxyvinyl)cuprate with allylic bromides occurs in good yield (eq 5).3,10 However, this reagent fails to give desired coupling products with saturated primary and secondary alkyl bromides, affording cuprate reagent self-coupling products; attempted opening of oxiranes was also unsuccessful.3

Related Reagents.

1-Ethoxyvinyllithium; Lithium (Z)-Bis(2-ethoxyvinyl)cuprate; Lithium Bis(1-methoxyvinyl)cuprate; Lithium Divinylcuprate.

1. Lipshutz, B. H.; Sengupta, S. OR 1992, 41, 135.
2. FF 1977, 6, 204.
3. (a) Boeckman, R. K., Jr.; Bruza, K. J.; Baldwin, J. E.; Lever, O. W., Jr. CC 1975, 519. (b) Boeckman, R. K., Jr.; Bruza, K. J. JOC 1979, 44, 4781.
4. Trost, B. M.; Ohmori, M.; Boyd, S. A.; Okawara, H.; Brickner, S. J. JACS 1989, 111, 8281.
5. (a) Schöllkopf, U.; Hänßle, P. LA 1972, 763, 208. (b) Baldwin, J. E.; Höfle, G. A.; Lever, O. W., Jr. JACS 1974, 96, 7125. (c) Gschwend, H. W.; Rodriguez, H. R. OR 1979, 26, 1.
6. Lever, O. W., Jr. T 1976, 32, 1943.
7. Kotick, M. P.; Leland, D. L.; Polazzi, J. O.; Schut, R. N. JMC 1980, 23, 166.
8. Fujiwara, S.; Smith, A. B., III TL 1992, 33, 1185.
9. Behling, J. R.; Babiak, K. A.; Ng, J. S.; Campbell, A. L.; Moretti, R.; Koerner, M.; Lipshutz, B. H. JACS 1988, 110, 2641.
10. Canonne, P.; Boulanger, R.; Angers, P. TL 1991, 32, 5861.

Christopher W. Alexander

Emory University, Atlanta, GA, USA

Robert K. Boeckman, Jr.

University of Rochester, NY, USA

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