Methylene transfer agents

D. L. Phillips, W.H. Fang, and X. Zheng, Isodiiodomethane is the methylene transfer agent in cyclopropanation reactions with olefins using ultraviolet photolysis of diiodomethane in solutions a density functional theory investigation of the reactions of isodiiodomethane, iodomethyl radical, and iodomethyl cation with ethylene. J. Am. Chem. Soc. 123(18), 4197-4203 (2001). 

An interesting, and potentially useful, approach to the synthesis of optically active cyclopropanes is by the use of chiral iron complexes (XLVI) as methylene transfer agents to olefins (Davison et al, 1974). Reaction of XLVI with 1-phenyl-1-propene under acidic conditions affords (— )- lR,2R) trans-2-methylphenylcyclopropane (26% enantiomeric excess). 

Methylene ( CH2), the simplest carbene, can be prepared by decomposition of the highly toxic and explosive reagent diazomethane (CH Nj). However, more easily used reagents have been developed that, while they do not produce methylene directly, function as methylene transfer agents. They are called carbenoid species because they react like carbenes. lodomethylzinc iodide, known as the Simmons-Smith reagent, is a carbenoid. In the Simmons-Smith method, diiodomethane reacts with a zinc-copper alloy to produce an intermediate I—CH Zn—I compound. 

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