Chloroform halogens + olefins

The base-promoted a eliminations of chloroform or bromoform provide a simple method for the production of dihalocarbenes. These add readily to olefinic double bonds to give 1,1-dihalocyclopropanes. The halogens can be removed (one or both) by reduction the most common method is to use tri-n-butyltin hydride. 

Also, psudo-P-D-mannopyranose (115) has been synthesized from 99 by the following reactions [28], Halogenation of 99 with triphenylphosphine, imidazole and iodine gave 1 L-4-0-benzyl-3-deoxy-3-iodo-1,2 5,6-di-0-isopropylidene-a//o-inositol (106), m.p. 77.4 °C, [oc]p° —30.1° (chloroform). Treatment of 106 with lithium aluminium hydride-resulted in a formation of two endocyclic olefins (107) and (108) in an approximately 1 2 ratio. Oxidation of 108with dimethyl sulfoxide and oxalyl chloride gave the enone (109) as a syrup, [a] 0 —68.11° (chloroform). Stereoselective... 

Perhalomethanes function as halogenating agents also by addition to olefins. This reaction has been discovered by Joyce, Hanford and Harmon who have reported the telomer-ization of ethylene with CC14 or with chloroform in presence of free radical initiators (equation 83)638 639. 

Hypochlorous acid directly reacts with organic nucleophilic compounds (X = O, N, S) or via the intermediate formation of the chlorine cation Cl " (HOCl — OH-+ CC Gallard and Gunten 2002, Hanna et al. 1991). Such reactions might also explain the formation of halogenated organic compounds in soils from OM such as humic material where the volatile fraction (for example chloroform) emits into air. All olefinic hydrocarbons and aromatic compounds add Cl and OH from HOCl (see for example reaction 5.422). 

Bromine readily adds to a double bond at -20 to 20 C to give dibromides in high yield, e.g., allyl bromide gives 98% 1,2,3-tribromo-propane. Chloroform, carbon tetrachloride, acetic acid, or ether are recommended solvents for the addition of halogen to olefins. Heat or sunlight favors dehydrohalogenation reactions. 

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