Magnesium Hydride-Copper(I) Iodide


[7693-27-8]  · H2Mg  · Magnesium Hydride-Copper(I) Iodide  · (MW 26.33) (CuI)

[7681-65-4]  · CuI  · Magnesium Hydride-Copper(I) Iodide  · (MW 190.45)

(in situ prepared hydridocopper reagent; reduces alkynes stereoselectively to cis-alkenes1)

Physical Data: prepared in situ.

Preparative Method: a slurry of MgH2 (4 mmol)1,2 in THF is added via syringe into a mixture of alkyne (1 mmol) and Copper(I) Iodide (4 mmol) at -78 °C under an inert atmosphere. The cooling bath is removed and the reaction temperature is allowed to warm slowly to rt. The mixture becomes a deep black color with slight effervescence. After stirring for 24-48 h the reaction is quenched with water and the aqueous layer is extracted with THF. The combined organic extract is dried over MgSO4.


The reagent reduces terminal alkynes to the corresponding alkenes (alkanes were not detected) with 100% selectivity in 80-98% yield. Internal alkynes are reduced only to the cis-alkene (no trans-alkene or alkane detected) in 80-95% yield (Table 1).


Copper(I) t-Butoxide can be substituted for copper(I) iodide.1

Alternative Methods.

The reduction of alkynes to cis-alkenes can be accomplished by many other methods, such as catalytic hydrogenation,3,4 dialkylaluminum hydride,5,6 or Hexa-m-hydrohexakis(triphenylphosphine)hexacopper.7 See also Copper(I) Bromide-Lithium Trimethoxyaluminum Hydride.

1. Ashby, E. C.; Lin, J. J.; Goel, A. B. JOC 1978, 43, 757.
2. Goel, A. B.; Ashby, E. C. ICA 1984, 87, 61.
3. Lindlar, H. HCA 1952, 35, 446.
4. Rylander, P. N. Catalytic Hydrogenation in Organic Synthesis; Academic: New York, 1979.
5. Wilke, G.; Müller, H. CB 1956, 89, 444.
6. Eisch, J. J.; Kaska, W. C. JACS 1966, 88, 2213.
7. Daeuble, J. F.; McGettigan, C.; Stryker, J. M. TL 1990, 31, 2397.

Ronald K. Russell

The R. W. Johnson Pharmaceutical Research Institute, Raritan, NJ, USA

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