Furukawa reagent

The solution structure of the Furukawa reagent (EtZnCH2l) has been established by H and NMR as well . This reagent is in equilibrium with Et2Zn and Zn(CH2l)2 (equation 12), but it has a limited lifetime it will either undergo cyclopropanation or it will rearrange to PrZnI. 

The level of diastereoselection in the cyclopropanation of chiral acyclic E-aUylic alcohols is highly dependent upon the choice of the reagent, the stoichiometry and the solvent. Charette has shown that, with simple ii-substituted chiral allylic alcohols, the use of an excess of the Furukawa reagent in dichloromethane provided the highest syn stereocontrol (equation 59). ... 

An alternative to the Simmons-Smith and Furukawa reagents is iodomethylzinc phenoxide, readily accessible by deprotonation of phenol with Et2Zn and subsequent metal-halogen exchange with CH2l2- An economically attractive method for cyclopropanation of alkenes is to use CH2Br2, which is considerably less expensive and easier to purify and store than CH2l2- ... 

Allylic alcohols undergo cyclopropanation faster than unfunctionalized alkenes, " and excellent diastereoselectivities have been observed in reactions of the Furukawa reagent with acyclic chiral allylic alcohols. ... 

Conversion of Alcohols to Alkenes. Furukawa and coworkers found that treatment of alcohols with MsCl/DM AP/H2O/ CH2CI2 (Furukawa reagent) produces the dehydrated products in good yields (eq 1). In the absence of water, the dehydrated products can still be formed, but in very poor yield. Some examples of secondary alcohols undergoing this elimination have also been reported (eq 7) ... 

Preparative Methods for the synthesis of the parent and the 2-monoalkyl-substituted compounds, reduction of ethyl 3-chloropropionate with sodium-potassium alloy in the presence of chlorotrimethylsilane in ether. A recent modification using ultrasound irradiation is much more convenient and more widely applicable. Other substituted derivatives are prepared by cyclopropanation of alkyl silyl ketene acetals with the Furukawa reagent (diiodomethane/diethylzinc). ... 

The possibility of a radical mechanism is supported by the observation of the accelerating effect of molecular oxygen on the cyclopropanation. Miyano et al. discovered that the addition of dioxygen accelerated the formation of the zinc carbenoid in the Furukawa procedure [24a, b]. The rate of this process was monitored by changes in the concentration of ethyl iodide, the by-product of reagent formation. Comparison of the reaction rate in the presence of oxygen with that in the... 

The use of iodoform as the reagent precursor under Furukawa s conditions gives rise to a more complex scenario, since the additional C—I bonds can further react with an ethylzinc species (equation 8)" . The reaction of the iodo-substituted zinc carbenoid with an alkene will generate an iodo-substituted cyclopropane, whereas that involving the gem-dizinc carbenoid will lead to a cyclopropylzinc product. The evidence for the formation of a. gem-dizinc carbenoid was obtained not only by the analysis of the cyclopropanation products but also by the formation of rfi-iodomethane upon quenching the reagent with D2O/DCI. 

There are a number of modifications of this reaction all providing the same product Furukawa s Reagent EtjZn + ICH2I (1 1)... 

Furukawa, N. Ogawa, S. Matsumura, K. Fuji-hara, H. Extremely facile ligand-exchange and disproportionation reactions of diaryl sulfoxides, selenoxides, and triarylphosphine oxides with organolithium and Grignard reagents. 

More sophisticated methods to prepare various halomethylzinc reagents that avoid pre-activation of one of the precursors are also available. One of the most practical method to prepare these electrophilic halomethylzinc reagents has been disclosed by Furukawa and co-workers.15 They found that... 

Preparation of the Furukawa s reagent (EtZnCH2l) syn-diastereoselective cyclopropanation of chiral acyclic allylic alcohols16... 

Fig. 3.16. Two reactions that demonstrate the stereospecificity of n s-cycLopropanations with the Simmons-Smith reagent. In the first reaction the zinc carbenoid is produced according to the original method, and in the second it is produced by the Furukawa variant.

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