[13146-23-1]  · C8H5Cu  · Phenylethynylcopper(I)  · (MW 164.68)

(mild nucleophilic agent for the introduction of the phenylethynyl group,2 formation of phenylallenes,3 and Glazer cross-coupling products4)

Alternate Name: copper(I) phenylacetylide.

Physical Data: bright yellow solid, mp 229 °C;5a IR n(C&tbond;C) 1933 cm-1.5a Vibrational spectra have been reported.5b

Solubility: sol pyridine, THF, ether, acetonitrile, hot cyclohexane, dioxane; insol water.

Analysis of Reagent Purity: gravimetric analysis of derived salts.9 Traces of ammonia are reported to impart a green tinge to the solid.

Preparative Methods: (i) phenylacetylene is treated with either ammoniacal Copper(II) Sulfate and Hydroxylamine hydrochloride (reductant)6 or Copper(I) Iodide in ethanol;7 (ii) phenylacetylene is lithiated, then treated with copper(I) iodide; (iii) phenylacetylene is treated with Copper(I) t-Butoxide.8 Drying: heat (65 °C) under vacuum.

Handling, Storage, and Precautions: all copper(I) acetylides are potentially explosive in the solid state. Use in a fume hood.

Alkynic Couplings.

Copper(I) phenylacetylide participates in efficient coupling with a range of aryl iodides and bromides to give substituted tolanes2,6,7,10,11 which, if possessing an ortho amino or hydroxy group, can be thermolyzed to yield 2-phenylbenzofurans, -indoles, and -furo[3,2-b]pyridines (eq 1).12 The reactions are usually conducted in refluxing DMF or pyridine (see also 3-Methyl-3-buten-1-ynylcopper(I), 1-Hexynylcopper(I), 1-Pentynylcopper(I)).

Application of the cross-coupling sequence has been extended to bromo quinones, where milder conditions ensuing from use of a palladium catalyst (eq 2) allow this transformation to proceed with ease and high efficiency (77% yield).13

Coupling to acyl chlorides is reported to be facile (eq 3),14 allowing direct access to a-alkynones. The couplings are promoted by Lithium Iodide, as lithium chloride was found to be inferior;14 in some cases addition of Hexamethylphosphorous Triamide is necessary.15 This protocol has been applied in the synthesis of natural products.16 By forming copper(I) phenylacetylide in situ using phenylacetylene and Copper(I) Bromide in the presence of Diisopropylamine, intermolecular addition to formaldehyde has been demonstrated, giving a potentially versatile route to other substituted allenes (eq 4).3 Under oxidative conditions, it is possible to couple copper(I) acetylides to form (in this instance) diphenylbutadiyne. The procedure, known as the Glaser coupling, has been reported to proceed either in solution or in the solid state.4 It is also possible to couple copper(I) phenylacetylide with cyanogen bromide to form phenylpropynenitrile,17 and with alkylcopper reagents to form disubstituted alkynes.18 Nucleophilic addition of copper phenylacetylide to organotungsten complexes proceeds with regiocontrol (eq 5), giving ultimate access to enynes.19

Other applications of copper(I) phenylacetylide include 2-phenylethynylation of N-benzyloxypyridinium salts,20 [3 + 2] cycloaddition to nitrones (which gives mixtures of azetidin-2-ones: see 1-Hexynylcopper(I)),21 nucleophilic addition to the tetrathiatriazepinium cation,22 and coupling to activated amines to yield terminal N,N-dialkylalkynic amines.23

Related Reagents.

3,3-Dimethyl-1-butynylcopper(I); Phenylethynylcopper(I)-Tris(tributylphosphine).

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 1974, 4, 101. (e) FF 1979, 7, 237. (f) FF 1986, 12, 143.
2. Castro, C. E.; Stephens, R. D. JOC 1963, 28, 2163.
3. Searles, S.; Li, Y.; Nassim, B.; Lopes, M. T. R.; Tran, P. T.; Crabbe, P. JCS(P1) 1984, 747.
4. Toda, F.; Tokumaru, Y. CL 1990, 987.
5. (a) Okamoto, Y.; Kundu, S. K. J. Phys. Chem. 1973, 77, 2677. (b) Aleksanyan, V. T.; Garbuzova, I. A.; Golding, I. R.; Sladkov, A. M. Spectrochim. Acta 1975, 31A, 517.
6. Castro, C. E.; Gaughan, E. J.; Owsley, D. C. JOC 1966, 31, 4073.
7. Stephens, R. D.; Castro, C. E. JOC 1963, 28, 3313.
8. Tsuda, T.; Hashimoto, T.; Saegusa, T. JACS 1972, 94, 658.
9. Straus, F. LA 1905, 342, 190.
10. Clive, D. L. J.; Angoh, A. G.; Bennett, S. M. JOC 1987, 52, 1339.
11. (a) Korshunov, S. P.; Katkevich, R. I.; Vereshchagin, L. I. ZOR 1967, 3, 1327. (b) Bossenbroek, B.; Sanders, D. C.; Curry, H. M.; Shechter, H. JACS 1969, 91, 371.
12. Owsley, D. C.; Castro, C. E. OS 1972, 52, 128; OSC 1988, 6, 916.
13. Clive, D. L. J.; Khodabocus, A.; Vernon, P. G.; Angoh, A. G.; Bordeleau, L.; Middleton, D. S.; Lowe, C.; Kellner, D. JCS(P1) 1991, 1433.
14. Normant, J. F.; Bourgain, M. TL 1970, 2659.
15. Bourgain, M.; Normant, J. F. BSF(2) 1973, 2137.
16. Lewis, M. D.; Duffy, J. P.; Heck, J. V.; Menes, R. TL 1988, 29, 2279.
17. Compagnon, P. L.; Grosjean, B. S 1976, 448.
18. Levene, R.; Becker, J. Y.; Klein, J. JOM 1974, 67, 467.
19. Cheng, M. H.; Ho, Y. H.; Lee, G. H.; Peng, S. M.; Liu, R. S. CC 1991, 697.
20. Nishiwaki, N.; Minakata, S.; Komatsu, M.; Ohshiro, Y. CL 1989, 773.
21. For example, see Ding, L. K.; Irwin, W. J. JCS(P1) 1976, 2382.
22. Dunn, P. J.; Rees, C. W. JCS(P1) 1989, 2489.
23. Boche, G.; Bernheim, M.; Niessner, M. AG(E) 1983, 22, 53.

Graham B. Jones & Brant J. Chapman

Clemson University, SC, USA

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