[66769-63-9]  · C6H9CuO  · (3-Methoxy-3-methyl-1-butynyl)copper(I)  · (MW 160.70)

(nontransferable ligand used in cuprate preparation for selective ligand transfer to electrophiles2)

Physical Data: red solid.

Solubility: sol THF; moderately sol ether (0.1 M at 0 °C); insol hexane, H2O.

Preparative Methods: lithiation of 3-methoxy-3-methyl-1-butyne followed by addition of Copper(I) Iodide. Usually prepared and used in situ. Copper(I) acetylides can be stored under water, then dried in the air.

Handling, Storage, and Precautions: copper(I) acetylides are reported to be explosive when dry. Prepared reagent should be used within a few days for best results. Use in a fume hood.

Mixed Organocuprates.

Since their introduction by Corey in 1972,3 mixed organocuprates of composition [RC&tbond;CCuRt]Li have received widespread use for their ability (when Rt is sp2- or sp3-bound to Cu) to effect selective transfer of Rt to suitable electrophiles.2 Of the range of organocuprates which have been investigated for use as nontransferable4 or dummy ligands, cuprates derived from 3-methoxy-3-methyl-1-butynylcopper are among the most attractive (see also 3,3-Dimethyl-1-butynylcopper(I), 1-Hexynylcopper(I), and 1-Pentynylcopper(I)-Hexamethylphosphorous Triamide). This stems from a combination of their high solubility in traditional solvents for coupling reactions (ether, THF), and the economy of using an inexpensive alkynic precursor.2 Treatment of the alkyne with the requisite organolithium species yields synthetically useful lithium organocuprate derivatives (eq 1).

Mixed Alkyl Cuprates.

Mixed alkyl cuprates will selectively alkylate alkyl halides in moderate yield (eq 2).2 Higher yields have been reported for alkyl transfer by converting the cuprate into a lithium dialkylcuprate, which transfers one alkyl group.5 Alkyl delivery to cycloalkenones (eq 3)2 and epoxides6 is efficient, and near-quantitative yields are obtained using a variety of alkyl donors.

Mixed Alkenyl and Aryl Cuprates.

Delivery of alkenyl and aryl groups is probably the most versatile and celebrated application of mixed cuprates containing this dummy ligand. A variety of excellent examples demonstrate the high degree of efficiency of the process;7-11 the heavily substituted nature of many of the combining species is a testimony to the tolerance of such mixed cuprates. The 3-methoxy-3-methyl-1-butynyl ligand was found to be clearly superior to a phenylthio dummy ligand in a variety of vinylcopper species.10 SN2 addition sequences are also possible, giving highly functionalized products (eq 4).12 Asymmetric induction (up to 92% ee) has been reported for the conjugate addition of the mixed lithiocuprate derived from the anion of methyl norephedrine acetone imine to cycloalkenones.13,14

Trimethylstannylcopper Reagents.

Treatment of Trimethylstannyllithium with 3-methoxy-3-methyl-1-butynylcopper results in formation of the corresponding trimethylstannylcopper species (eq 5).15 Such reagents are, as predicted, able to chemoselectively transfer the nondummy ligand to an electrophile. Thus, addition of a stannylcopper species to alkynes results in formation of (E)-alkenes (eq 5) with very high selectivity.

Related Reagents.

For lithium dialkylcuprates, see Lithium Dimethylcuprate; for phenylthio mixed cuprates, see e.g. Lithium Methyl(phenylthio)cuprate and Phenylthiocopper(I). Also see Lithium (1-Hexynyl)(2-tri-n-butylstannylvinyl)cuprate, Lithium (1-Pentynyl)(2-tri-n-butylstannylvinyl)cuprate, Lithium Phenylthio(trimethylstannyl)cuprate, Tri-n-butylstannylcopper, and Trimethylstannylcopper-Dimethyl Sulfide.

1. (a) Normant, J. F. S 1972, 63. (b) Sladkov, A. M.; Gol'ding, I. R. RCR 1979, 48, 868. (c) Lipshutz, B. H.; Sengupta, S. OR 1992, 41, 135. (d) FF 1980, 8, 324. (e) FF 1981, 9, 300.
2. Corey, E. J.; Floyd, D.; Lipshutz, B. H. JOC 1978, 43, 3418.
3. Corey, E. J.; Beames, D. JACS 1972, 94, 7210.
4. For additional discussions on the origin of selective ligand release, see: (a) Mandeville, W. H.; Whitesides, G. M. JOC 1974, 39, 400. (b) Westmijze, H.; Meijer, J.; Bos, H. J. T.; Vermeer, P. RTC 1976, 95, 299.
5. Lipshutz, B. H.; Wilhelm, R. S.; Floyd, D. M. JACS 1981, 103, 7672.
6. Prandi, J.; Beau, J-M. TL 1989, 30, 4517.
7. Corey, E. J.; Bock, M. G.; Kozikowski, A. P.; Rama Rao, A. V.; Floyd, D.; Lipshutz, B. TL 1978, 1051.
8. Corey, E. J.; Hopkins, P. B.; Kim, S.; Yoo, S.; Nambiar, K. P.; Falck, J. R. JACS 1979, 101, 7131.
9. Murakami, M.; Matsuura, T.; Ito, Y. TL 1988, 29, 355.
10. (a) Majetich, G.; Leigh, A. J.; Condon, S. TL 1991, 32, 605. (b) Majetich, G.; Leigh, A. J. TL 1991, 32, 609.
11. Saimoto, H.; Kusano, Y.; Hiyama, T. TL 1986, 27, 1607.
12. Baudouy, R.; Sartoretti, J. T 1983, 39, 3293.
13. Yamamoto, K.; Kanoh, M.; Yamamoto, N.; Tsuji, J. TL 1987, 28, 6347.
14. For the origin of such asymmetric transfer, see: Corey, E. J.; Naef, R.; Hannon, F. J. JACS 1986, 108, 7114.
15. (a) Piers, E.; Chong, J. M.; Morton, H. E. TL 1981, 22, 4905. (b) Piers, E.; Chong, J. M. JOC 1982, 47, 1602.

Graham B. Jones & Brant J. Chapman

Clemson University, SC, USA

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