[557-20-0]  · C4H10Zn  · Diethylzinc-Iodoform  · (MW 123.50) (CHI3)

[75-47-8]  · CHI3  · Diethylzinc-Iodoform  · (MW 393.73)

(combination reagent for monoiodocarbene formation and cyclopropanation)

Physical Data: Et2Zn: mp -28 °C; bp 117 °C; d 1.205 g cm-3. CHI3: mp 120-123 °C; d 4.008 g cm-3.

Solubility: sol alkene substrates.

Preparative Method: prepared in situ by addition of iodoform to a mixture of alkene and diethylzinc.

Handling, Storage, and Precautions: diethylzinc is pyrophoric and moisture sensitive. Iodoform is toxic and an irritant.

General Discussion.

The reaction of cyclohexene with the monoiodocarbene generated from the action of Diethylzinc on Iodoform in light petroleum produced a mixture of stereoisomeric monoiodocyclopropanes. The yield was only 10% for this reaction.1 It was later found that the reaction was highly dependent on the concentration of the alkene and the temperature. If the reaction was performed with the alkene as the solvent and the temperature lowered to 0 °C, it produced a 70% yield of a mixture of cyclopropyl iodides (eq 1).2 The lowered yield and altered ratio of syn:anti isomers was attributed to the thermal instability of the syn isomer. The reaction of n-butyl vinyl ether resulted only in the formation of polymeric material. None of the cyclopropyl derivative was observed.

The reaction of diethylzinc and iodoform in benzene produces ethylcycloheptatriene in 48% yield (eq 2). The reaction is believed to proceed via the tropylium cation, which undergoes subsequent transformation to the ethyl substituted product by further reaction with Ethylzinc Iodide. If toluene was used in place of benzene, a mixture of the three regioisomeric cycloheptatrienes was formed.3

An investigation of the stereoselectivity of the iodocyclopropanation process has shown that for cycloalkenes the ratio of syn:anti isomers increases as the ring size increases. For cyclopentene, only the anti isomer was obtained due to decomposition of the syn isomer. Cyclohexene produces a 0.63:1.0 syn:anti ratio in 40% yield. The syn-iodocyclopropane predominates in a ratio of 3.8:1 for the reaction with cycloheptene. Only the syn compound was produced with cyclooctene, but the yield was only 18% (eq 3). The photolysis of iodoform in the presence of cyclooctene provides the same compound in 72% yield. Cyclodecene and cyclododecene also afford only the syn adducts.4

For the acyclic diene cis-2-butene, the stereochemical integrity of the methyl groups was maintained in the final iodocyclopropane (eq 4). In this case, only the syn product was formed.

Related Reagents.


1. Nishimura, J.; Furukawa, J. CC 1971, 1375.
2. Miyano, S.; Hashimoto, H. BCJ 1974, 47, 1500.
3. (a) Miyano, S.; Hashimoto, H. CC 1973, 216. (b) Miyano, S.; Hashimoto, H. BCJ 1973, 46, 3257.
4. Dehmlow, E. V.; Stütten, J. TL 1991, 32, 6105.

Michael J. Taschner

University of Akron, OH, USA

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