[557-20-0]  · C4H10Zn  · Diethylzinc-Bromoform-Oxygen  · (MW 123.50) (CHBr3)

[75-25-2]  · CHBr3  · Diethylzinc-Bromoform-Oxygen  · (MW 252.73)

(cyclopropanation reagent1)

Preparative Method: the reaction of bromoform with diethylzinc generates dibromomethylzinc bromide in situ.1

Handling, Storage, and Precautions: the reagent cannot be stored and should be used directly after its preparation.

Cyclopropanation Reactions.

The treatment of Diethylzinc and Bromoform with an alkene in the presence of Oxygen produces monobromocyclopropanes in good yields (eq 1).1 Low yields are obtained if no oxygen is passed through the reaction mixture. The cyclopropanation of cis-cyclooctene (see Iodomethylzinc Iodide) and cis-2-butene give syn-bromocyclopropanes with high stereoselectivity (eqs 2 and 3).1 Styrene was found to inhibit the cyclopropanation, suggesting a radical reaction. A related system can also be used to perform a ring expansion of alkylbenzenes (eq 4).1 The reaction is possible with Diethylzinc-Iodoform, leading to ethylated cycloheptatrienes.2 A novel cyclopropanation is observed by reacting bromoform and diethylzinc with ketene acetals, leading to spiro- and bicyclic esters in good yields (eqs 5 and 6).3 If no allylic hydrogen or unsaturation is present in the molecule, a different reaction is observed (eq 7).3 The new cyclopropanation procedure has been applied in a synthesis of (±)-sabinene (1) (eq 8).3

1. Miyano, S.; Matsumoto, Y.; Hashimoto, H. CC 1975, 364.
2. (a) Miyano, S.; Hashimoto, H. BCJ 1973, 46, 3257. (b) Miyano, S.; Hashimoto, H. CC 1971, 1418. (c) Miyano, S.; Hashimoto, H. BCJ 1973, 46, 892. (d) Miyano, S.; Yamashita, J.; Hashimoto, H. BCJ 1972, 45, 1946.
3. Rousseau, G.; Slougui. N. JACS 1984, 106, 7283.

Paul Knochel

Philipps-Universität, Marburg, Germany

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