Gem-Dichloroalkanes

The easy three-fragment, four-electron oxidative addition of chloroform and gem-dichloroalkanes to [Rh(/ -pz)(f-BuNC)2]2, 72, were prepared in good yield by replacement of cod in [Rh(/x-pz)(cod)]2 (91, 92), yielding functionalized methylene bridged complexes (93). Thus, molecules such as CHC12R (R = H, Ph, COOMe, or Cl) react with Complex 72 to yield mainly [ Rh(/i-pz)Cl(/-BuNC)2 2(/i-CHR)] and [Rh(p-pz)Cl(f-BuNC)2l2 as side products. A definitive proof of the structure of the methylene-bridged complexes comes from their H and l3C NMR spectra (93). No intermediates were observed in these reactions. 

Recently, the reactions of both gem-dichloroalkanes (213, HIg-Cl) and vinyl chlorides (220, HIg-Cl) with nitriles were reported. These reactions proceed via the highly active chlorocarbeniura intermediates 226. 

The reaction of oximes with elemental chlorine is known. In the presence of a Lewis acid, gem-dichloroalkanes 7 are obtained.13... 

Tordeux M, Boumizane K, Wakeelman C (1993) Preparation of gem-dichloroalkanes from oximes. J Org Chem 58 1939-1940... 

Aliphatic gem-dihalides require more vigorous conditions for hydrolysis than do the benzal halides. Examples are found in the treatment of certain 1,1-dichloroalkanes, like l,l-dichloro-3 methylbutane and 1,1-dichloro-3,3"dimethylbutane, with water and, in some cases, magnesium oxide for 4 hours at 200-300°. The aldehydes are formed in 60-96% yields (cf. method 222). 

Chlorination of phosphines. Both trialkyl- and triarylphosphines afford the dichlorides on reaction with triphosgene, which can then be used to convert epoxides to 1,2-dichloroalkanes, aldehydes to gem-dichlorides, amides to nitriles, formamides to isonitriles, ureas to carbodiimides, and amines to triphenylphosphoranylimines. 

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