1.1- Dihalocyclopropanes

PTC has also found application in organometallic chemistry, for example, in metal-catalyzed carbonylation of alkyl or aryl halides. Interestingly, some reactions are found to occur in PTC systems that do not work under normal synthetic reaction conditions. 

The above mentioned simple examples of the application of PTC technology illustrate its substantial potential advantages in comparison with traditional processes. There are hundreds other possible industrial applications of PTC for a 

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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. 

Haloforms react with potassium /-butoxide to form dihalocarbenes, which add smoothly to olefins giving 1,1-dihalocyclopropanes (2). The reaction does not appear... 

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 treatment of 1,1-dihalocyclopropanes by methyllithium appears to be a general route to allenes, providing the product is not highly strained. An example is shown in the reaction (13). The procedure given below employs the reaction for the preparation... 

Much of the literature regarding dihalocarbenes is concerned with reactions of CX2 with olefinic substrates to give 1,1-dihalocyclopropane derivatives. These reactions occur with retention of stereospecificity, as expected for singlet carbenes. Dihalocarbenes also exhibit strong electrophilic behavior towards olefins, and will often not react with weakly nucleophilic species if stronger nucleophiles are present. 

Several 1,1-dihalocyclopropanes have been prepared242-246 by addition of dihalocarbenes to double bonds in heterocyclic molecules. 

In this chapter we will be concerned with only 1,1-dihalocyclopropanes and these will be referred to as dihalocyclopropanes throughout the text. 

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