This reaction affords the cyclopropanation of olefins.
Mechanism of the Simmons-Smith Reaction
Ultrasonication improves the rate of formation of these organozinc compounds, as with many organometallic reactions occurring at a surface.
The mechanism has not been fully clarified, but pure carbenes can be excluded, and a metal carbenoid is likely to be involved. The following results may be interpreted to indicate a possible complexation of the active species by hydroxy groups leading to reaction on the same face as this substituent. This would only be possible if an organozinc reagent is present.
Various research groups have developed variants of the Simmons-Smith cyclopropanating reagent through the replacement of the iodide ligand on the zinc atom with a strongly electron-withdrawing substituent. Whereas the original reagent often requires a directing group such as the hydroxyl of an allylic alcohol, carbenoids such as CF3CO2ZnCH2I and (PhO)2P(O)OZnCH2I enable a rapid cyclopropanation of alkenes without the need for such a directing group.
Preparation of a Storable Zinc Carbenoid Species and Its Application in Cyclopropanation, Chain Extension, and [2,3]-Sigmatropic Rearrangement Reactions
A. Voituriez, L. E. Zimmer, A. B. Charette, J. Org. Chem., 2010, 75, 1244-1250.
Highly Enantio- and Diastereoselective Tandem Generation of Cyclopropyl Alcohols with up to Four Contiguous Stereocenters
H. Y. Kim, A. E. Lurain, P. Garcia-Carcia, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc., 2005, 127, 13138-13139.