Phenyl trihalomethyl mercury Compounds

Dihalocarbenes from Phenyl(trihalomethyl)mercury Compounds 

Seyferth (7) discovered that phenyl(trihalomethyl)mercury compounds decompose when heated in a solvent giving dihalocarbenes. When the solvent contains a suitable olefin, carbene addition occurs giving 1,1-dihalocyclopropane derivatives. The reaction has the advantage that strong base is not required in the reaction mixture, and base- 

The preparation of the reagents, on the other hand, is somewhat involved and requires high-speed stirring (5). Given below, therefore, is an alternate method of preparation of phenyl(trichloromethyl)mercury that requires only conventional stirring (9). The use of this compound to prepare 7,7-dichloronorcarane is also given. 

It should be pointed out that the mono-, di-, and tribromo derivatives of the reagent all react considerably more rapidly than the trichloro reagent. For example, the tribromo compound reacts with cyclohexene in about 2 hours, while the trichloro compound requires 36 to 48 hours (7), 

Fieser and M. Fieser, Advanced Organic Chemistry, p. 536. Reinhold, New York, 1961. 

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More useful for synthetic purposes, however, is the combination of the zinc-copper couple with methylene iodide to generate carbene-zinc iodide complex, which undergoes addition to double bonds exclusively to form cyclopropanes (7). The base-catalyzed generation of halocarbenes from haloforms (2) also provides a general route to 1,1-dihalocyclopropanes via carbene addition, as does the nonbasic generation of dihalocarbenes from phenyl(trihalomethyl)mercury compounds. Details of these reactions are given below. 

III. Dihalocarbenes from Phenyl(trihalomethyl)mercury Compounds... 

The thermal decomposition of phenyl(trihalomethyl)-mercury compounds, C6H5.Hg.CX3, in the presence of olefins yields the dihalo-cyclopropane virtually quantitatively. A typical example is expressed in equation (15). The initial rate of disappearance of the organometallic... 

Seyferth, D. 1972. Phenyl(trihalomethyl)mercury compounds. Exceptionally versatile dihalocarbene precursors. Acc Chem Res 5, 65-74. 

Tor a review of the use of phenyl(trihalomethyl)mercury compounds as dihalocarbene or dihalocarbenoid precursors, see Seyferth, D. Acc. Chem. Res. 1972, 5, 65. For a review of the synthesis of cyclopropanes with the use of organomercury reagents, see Larock, R.C. Organomercurcury Compounds in Organic Synthesis, Springer, NY, 1985, pp. 341-380. 

Review. The chemistry of phenyl(trihalomethyl)mercury compounds has been reviewed by Seyferth.1... 

Phenyl (trihalomethyl) mercury compounds as versatile dihalocarbene precursors, useful in synthesis of halocyclopropanes. 

Preparation.1 These organomercury compounds are prepared by the procedure used for synthesis of phenyl(trihalomethyl)mercury (This volume). 

Seyferth1 reports that phenyl(dihalocarbomethoxymethyl)mercury compounds, although more stable than the corresponding trihalomethyl analogs, are good sources of halocarbomethoxycarbenes. Thus, when phenyl(dibromocarbo-methoxymethyl)mercury is refluxed with cyclooctene (1) in chlorobenzene under nitrogen for 43 hours, phenylmercuric bromide is formed (87% yield) and the two... 

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