Polyhalogenated compounds additions

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

In recent studies, we have observed that the addition of a number of polyhalogenated compounds (see 15-17 for representative examples) greatly increases the rate of bleaching of poly(methylphenyl) silane 2 upon irradiation. This effect is dramatically demonstrated by comparison of Figures 3 and 7. For the example shown in Figure 7, <95% of the incident light (313 nm) is absorbed by the polymer. 

Other polyhalogenated compounds can be used with similar success. CpFe(CO)2 dimer leads to the formation of mixtures of lactones and esters when reacted with an alkene and methyl trichloroacetate [79] with the lactone being the major product (Scheme 3.10). Similar results were reported earlier by Freidlina and Velichko [80]. FeCl3 and Fe(CO)5 are both suitable for catalyzing the addition of methyl dibromoace-tate to electron-deficient alkenes such as methyl propenoate. It was observed that the ratio of products (acyclic vs. lactone) could be tuned by varying the reaction conditions. In all cases, the acyclic product is predominantly formed. Only in the presence of a co-catalyst such as N,N-dimethylaniline are small amounts of lactone observed. Noteworthy, elevated temperatures (above 100 °C) are necessary for this transformation. 

Antimony(lll) fluoride, " antiinony(lll) fluoride activated with pentavalent antimony salts [anlimony(V) fluoride, antimony(V) chloride, antimony(V) bromide, or by the addition of bromine or chlorine to form pentavalent antimony salts in situ], SbFjX, and antimony(V) fluoride substitute active halogens. In general, antimony fluorides can substitute halogens in polyhalogenated compounds when more than one possible site of fluori-natioii is present, the following order of reactivity is observed (where X = Br or C ) ... 

This catalytic sequence is known as Kharasch addition or atom transfer radical addition (ATRA) [4]. Various polyhalogenated compounds such as CCI4 and CCI3CO2R are used as the organic halides, and transition metal salts or complexes are used as the catalyst [3]. Intramolecular version of the Kharasch addition reaction (atom transfer radical cyclization, ATRC) has opened novel synthetic protocols to the synthesis of carbocyde or heterocyles catalyzed by transition metals [5-7], and this has become a very important field in free radical cydization in organic synthesis. Transition metal-catalyzed Kharasch reactions sometimes afford telomers or poly-... 

The discovery of Minisci et al.,39 Asscher and Vofsi,40 and others41 of the transition metal catalyzed addition of haloalkanes to alkenes by a redox chain process (Scheme 14) has found vast synthetic applications.830,89 A recent summary has been given by van Koten et al.90 Virtually any olefin can serve as the source of reactive unsaturation, and a variety of polyhalogenated compounds such as alkyl halides,... 

Certain metal carbonyls are very useful for the removal of halogens from polyhalogenated compounds. In these reactions, again, an oxidative addition step should be important. As shown below, carbenes 33>, cyclobutadiene 34>, and benzyne complexes 35> are formed by the dehalogenation reaction with metal carbonyls. 

Scheme 1. Kharasch addition of polyhalogenated compounds to alkenes.

Martin P, Eginhard S, BeUus D. Copper(I)-catalyzed radical additions of polyhalogenated compounds to olefins. Part 1. Synthesis of polyhalogenated hutyryl chlorides, precursors of pyrethroid haloketenes. Helv. Chim. Acta 1980 63 (7) 1947-1957. 

From the reaction products of the polyhalogenated ethanes and propanes shown in Table 13.7 we deduce that such halogenated compounds may react in aqueous solution by yet another type of reaction, so-called /3-elimination. In this reaction, in addition to the leaving group (L ), a proton is lost from an adjacent carbon atom (hence the prefix /3-) and a double bond is formed ... 

Oxazetidines have been obtained by [2 + 2] addition of nitroso compounds to appropriate alkenes. Trifluoronitrosomethane reacts with polyhalogenated ethylenes (69JCS(C)2ll9), with styrene (65JGU855) or with allenes (73JCS(Pi)l56l) to give oxazetidines (e.g. Scheme 7). 

Many polyhalogenated monoterpenes have potent biological activity (7). In addition to cytotoxic activity, several compounds display insect repellent and antifeedant activity, and selective insect cell toxicity (480). To acquire sufficient quantities of these and other target metabolites for biological evaluation, the laboratory cultivation of marine algae - bioprocess engineering - is under intense exploration (481 483). 

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