Ethylzinc Iodide1


[994-75-7]  · C2H5IZn  · Ethylzinc Iodide  · (MW 221.36)

(used in combination with CH2I2 for the cyclopropanation of alkenes (Sawada reaction);1 displays the typical reactions of an alkylzinc halide2)

Physical Data: mp 98 °C dec; polymeric in the solid state, monomeric in ether, THF, and ethyl iodide.

Solubility: sol hexane, toluene, ether, THF, amines.

Form Supplied in: not commercially available.

Preparative Methods: by the reaction of commercially available Diethylzinc and Zinc Iodide in many solvents,3 or directly from Ethyl Iodide and Zinc powder.4

Analysis of Reagent Purity: iodometric titration according to Job.5

Handling, Storage, and Precautions: ethereal solutions are stable for several months at 25 °C under an inert atmosphere, if contact with oxygen and moisture is avoided.

Cyclopropanation of Alkenes.

A wide range of alkenes and functionalized alkenes can be cyclopropanated by Diiodomethane and a Zinc/Copper Couple (Simmons-Smith reaction (see Diethylzinc and Iodomethylzinc Iodide)).1c The easy insertion of zinc into diiodomethane leads to iodomethylzinc iodide6 (ICH2ZnI), which is the actual cyclopropanation reagent.7 Diethylzinc8 (Furukawa reaction) and ethylzinc iodide9 (Sawada reaction) undergo a fast iodine-zinc exchange reaction with CH2I2, generating iodomethylzinc derivatives (eq 1). After the addition of an alkene, cyclopropanes are obtained in moderate to good yields (eq 2). A comparison between the three methods for generating iodomethylzinc-derived cyclopropanation reagents shows that the procedure using EtZnI often affords the best yields (Table 1).9

In some cases with the Sawada method the cyclopropanation succeeds, whereas the original Simmons-Smith procedure completely fails (eq 3).10 The best experimental procedure consists of heating an excess of an ethereal solution of ethylzinc iodide (ca. 4 equiv) with diiodomethane (1.2 equiv) for an hour, adding the alkene (1.0 equiv) at 0 °C, and stirring the reaction mixture at 25 °C for several hours. Under these conditions, alkenylsilanes can be cyclopropanated in high yields (eq 4).11

Other Uses.

Like other alkylzinc halides,11 ethylzinc iodide adds to aldehydes,4a although in moderate yields due to its low reactivity. Far better results are obtained when the reactions are performed in the presence of CuI salts.12 For example, reaction with cinnamyl chloride in the presence of catalytic Copper(I) Cyanide produces the allylated product (preferential SN2 substitution) in satisfactory yield (eq 5).13 Ethylzinc iodide has also been used for performing metathesis14 and aldol condensation15 reactions (eq 6), and as a polymerization16 catalyst.

1. (a) Furukawa, J.; Kawabata, N. Adv. Organomet. Chem. 1974, 12, 83. (b) Dictionary of Organometallic Compounds; Chapman & Hall: London, 1984. (c) Simmons, H. E.; Cairns, T. L.; Vladuchick, S. A.; Hoiness, C. M. OR 1973, 20, 1.
2. (a) Nützel, K. MOC 1973, 13/2a. (b) Carruthers, W. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 7, p 661.
3. Abraham, M. H.; Rolfe, P. H. JOM 1967, 7, 35.
4. (a) Gaudemar, M. BSF 1962, 974. (b) Couffignal, R. BSF 1972, 3543.
5. Job, A.; Reich, R. BSF 1923, 33, 1414.
6. (a) Seyferth, D.; Andrews, S. B. JOM 1971, 30, 151. (b) Seyferth, D.; Dertouzos, H.; Todd, L. JOM 1965, 4, 18. (c) Seyferth, D.; Vick, S. C. Synth. React. Inorg. Metal-Org. Chem 1974, 4, 515.
7. (a) Denmark, S. E.; Edwards, J. P.; Wilson, S. R. JACS 1991, 113, 723. (b) Denmark, S. E.; Edwards, J. P. JOC 1991, 56, 6974. (c) Denmark, S. E.; Edwards, J. P.; Wilson, S. R. JACS 1992, 114, 2592.
8. (a) Furukawa, J.; Kawabata, N.; Nishimura, J. TL 1966, 3353. (b) Furukawa, J.; Kawabata, N.; Nishimura, J. T 1968, 24, 53.
9. Sawada, S.; Inouye, Y. BCJ 1969, 42, 2669.
10. (a) Detty, M. R.; Paquette, L. A. JACS 1977, 99, 821. (b) Fitjer, L.; Kühn, W.; Klages, N.; Egert, E.; Clegg, W.; Schormann, N.; Sheldrick, G. M. CB 1984, 117, 3075.
11. Knochel, P. COS 1991, 1, 211.
12. (a) Knochel, P.; Yeh, M. C. P.; Berk, S. C.; Talbert, J. JOC 1988, 53, 2390. (b) Knochel, P.; Rozema, M. J.; Tucker, C. E.; Retherford, C.; Furlong, M.; AchyuthaRao, S. PAC 1992, 64, 361.
13. Ochiai, H.; Tamaru, Y.; Tsubaki, K.; Yoshida, Z. JOC 1987, 52, 4418.
14. (a) Levisalles, J.; Rudler, H.; Villemin, D. JOM 1980, 192, 195. (b) Devyatykh, G. G.; Danov, S. M.; Eremeev, I. V.; Polyakov, V. M.; Kvashennikov, A. I.; Moiseev, A. N. USSR Patent 1 293 184, 1987 (CA 1987, 107, 78 091).
15. Jpn. Patent 59 157 047, 1984 (CA 1985, 102, 78 437s).
16. (a) Kunio, K.; Nikki, M. U.S. Patent 3 590 010, 1971 (CA 1971, 75, 118 798t). (b) Kocheshkov, K. A.; Kargin, V. A.; Paleev, O. A.; Sheverdina, N. I.; Sogolova, T. I. CA 1964, 61, 5767e.

Paul Knochel

Philipps-Universität Marburg, Germany

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