Simmons-Smith-Furukawa reagent

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.

A number of modifications of the original Simmons-Smith cyclopropanation procedure have been reported. Furukawa s reagent, (iodomethyl)zinc derived from diethylzinc and diiodomethane, ° or its modification using chloroiodomethane instead of diiodomethane, ° allows more flexibility in the choice of solvent. The reagent is homogeneous and the cyclopropanation of olefins can be carried out in non-complexing solvents, such as dichloromethane or 1,2-dichloroethane, which greatly increase the reactivity of the zinc carbenoids. 

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- ... 

The more recently reported route to diethyl 3-oxoalkylhosphonates uses a zinc carbenoid-mediated approach, which is believed to proceed through the intermediacy of a cyclopropylzinc alkoxide. Thus, treatment of simple diethyl 2-oxoaIkylphosphonates with the Furukawa-modifled Simmons-Smith reagent provides a rapid and efficient preparation of 3-oxoalkyIphosphonates. The chain extension of simple, unfunctionalized P-ketophosphonates requires an excess (6 eq) of both Et2Zn and CH2I2 at room temperature. The presence of a-substitution on the 2-oxoalkylphosphonate does not diminish the efficiency of the reaction (see Section 7.2.3.7). 

CyclopropanationJ The title compound, prepared from ArOH, Et2Zn, and CH2I2, is a modified Simmons-Smith reagent, with which alkenes are transformed into cyclopropanes in excellent yields (6 examples, 90-98%). In terms of reactivity, the zinc phenoxide is comparable to bis(chloromethyl)zinc, but more reactive than bis(iodomethyl)zinc and Furukawa s reagent. 

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