[55630-32-5]  · C6H11CuSi  · 3-Trimethylsilyl-2-propynylcopper(I)  · (MW 174.81)

(agent for the introduction of the trimethylsilylpropynyl group via 1,6-conjugate additions2 and vinyl substitutions;3 preparation of lithium bis(trimethylsilylpropynyl)cuprate4)

Alternate Name: trimethylsilylpropargylcopper

Physical Data: brown heterogenous solution in ether.

Solubility: sol pyridine, THF; slightly sol ether.

Analysis of Reagent Purity: addition of aqueous ammonium chloride gives >95% conversion to 1-trimethylsilylpropyne.2

Preparative Method: a solution of 1-Lithio-3-trimethylsilyl-1-propyne containing N,N,N,N-Tetramethylethylenediamine (TMEDA) in ether2 or THF is added to a slurry of Copper(I) Iodide in ether at -78 °C, then warmed to -10 °C and used immediately.3

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

Coupling Reactions.

Trimethylsilylpropynylcopper adds to conjugated esters in a 1,6-manner if facilitated, giving mixtures of products dependent on the nature of the system.2 Addition to an unsubstituted (E)-dienoic ester gave an 8:2 mixture of allene:propynyl-substituted adducts (eq 1).

Best conversion yields (80%) are obtained by using 3.5 equiv of the copper reagent; use of 1.2 equiv results in a lower yield (42%) but an unaltered ratio.2 If a d-substituted dienoic ester is employed, the ratio reverses (eq 2), showing marked sensitivity to steric effects in this region;2 for best conversion to products (70%), 3.5 equiv of copper reagent are employed.2

Finally, if a b,g-disubstituted dienoic ester is used, selectivity reverses in favor of the allenic adduct (eq 3), pointing to the d-carbon as the single most important dictator of steric control in this reaction (in this sequence, only 1.2 equiv of cuprate were employed, accounting for the low (35%) overall conversion to products). Results obtained using t-butyldimethylsilylpropynylcopper paralleled those indicated above. As expected, however, the ratios of products showed sensitivity towards this more sterically bulky coupling agent, with a 95:5 ratio of allene:alkyne products in the addition to the unsubstituted dienoate (eq 1) and a 97:3 ratio of alkyne:allene in the addition to the d-substituted system (eq 2).2 Vinyl substitution has been reported, using an iodohexene and 2 equiv of trimethylsilylpropynylcopper; the corresponding adduct was obtained in 80% yield (eq 4).3 Using 1 equiv of copper acetylide, however, the yield drops to 63%. A mechanism has been proposed to account for this coupling, and is assumed to involve a four-centered transition state assembly.3


Lithium bis(trimethylsilylpropynyl)copper, prepared by addition of lithium trimethylsilylpropyne to copper(I) iodide, has been used as a nucleophilic source of the trimethylsilylpropynyl group (eq 5).4 Chemoselective 1,2-addition resulted in a 90% isolated yield of the desired secondary alkynyl alcohol (eq 5); use of the corresponding lithium or bromomagnesium acetylides resulted in substantial recovery of allenic products.4

Related Reagents.

1-Hexynylcopper(I); 1-Pentynylcopper(I); (Trimethylsilyl)ethynylcopper(I).

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 1977, 6, 638.
2. Ganem, B. TL 1974, 4467.
3. Commercon, A.; Normant, J.; Villieras, J. JOM 1975, 93, 415.
4. Vedejs, E.; Dent, W. H.; Gapinski, D. M.; McClure, C. K. JACS 1987, 109, 5437.

Graham B. Jones & Robert S. Huber

Clemson University, SC, USA

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