Vinylic halides conversion

In a conversion that is formally similar, substituted alkenes (CH2=CH—Y Y = R, COOMe, OAc, CN, etc.) can be dimerized to substituted alkanes CH CHYCHYCH, by photolysis in an H2 atmosphere, using Hg as a photosensitizer.4W Still another procedure involves palladium-catalyzed addition of vinylic halides to triple bonds to give 1,3-dienes.4V)... 

Run 116/KOH/vinyl halide molar ratio time (hr) Temp. (°C) Conversion of 116 (%) Yield (%) ... 

This result may also give a partial explanation for the known ozone stability of polymers containing vinyl halide moieties. Part of this inertness is undoubtedly the result of the slow ozone attack. However, this phenomenon can only impart a prolonged ozone resistance, while the conversion of the original double bond into single bonds could impart a permanent ozone resistance. We are extending our research to further model compounds of such polymer microstructures to find out whether... 

Hydroxymethylation of organic halides can bt effected by metal-catalyzed cross-coupling with the Grignard reagent (diisopropoxymcthylsilyl)methylmagnesium chloride (1) followed by oxidation. This two-step process i- particularly useful for regio- and ster-eocontrolled conversion of vinyl halides into al.ylic alcohols and of allylic halides into homoallylic alcohols. ... 

The first example of the use of the catalytic one-pot procedure described above, in which the deselenenylation occurs with substitution, is represented by the conversion of vinyl halides into a-alkoxy acetals [116]. This is illustrated in Scheme 38 in the case of -bromostyrene 235. The regioselective methoxy-selenenylation affords the a-bromo selenide 236, which undergoes a rapid solvolysis, through a selenium-stabilized carbocation to produce the selenide 237. Oxidation of this alkyl phenyl selenide with ammonium persulfate produces an oxygen stabilized carbocation, which affords the final product 238, and, at the same time, regenerates the selenenylating agent. 

Scheme 38. Phenylselenyl Sulfate Catalyzed One-Pot Conversions of Vinyl Halides into Alkoxy Acetals and of Styrene Derivatives into 1,1- and 1,2-Dialkoxy Alkanes...

Another non-isohypsic transformation, addition of halogens to a double bond, is probably the oldest known reaction of unsaturated compounds. It is widely used for both industrial and laboratory purposes. The products formed, 1,2-dihaloalkanes, are valuable for conversion into vinyl halides (such as vinyl chloride monomers for the production of PVC) or alkynes ... 

Vinyl halides represent yet another important class of intermediates in the conversion of ketones to alkenes. The most widely applied conditions for the conversion of ketones into vinyl halides are those developed by Barton et a/. ° for the conversion of 3p-acetoxyandrost-5-ene-17-one into 3P-hydroxyandrosta-5,16-diene (Scheme 44). These conditions of vinyl halide formation and subsequent reduction have been useful in a number of steroid systems for the introduction of a A -carbon-carbon double bond and have been shown to be compatible with such functional groups as alcohols, isolated double bonds and acetals. The scope of vinyl iodide formation from hydrazones has been studied by Pross and Stemhell, and recently the original reaction conditions were improved by using sterically hindered guanidine bases rather than triethylamine. Haloalkenes have also been prepared from the corresponding ketones by treatment with iodoform and chromium chloride or with phosphorous penta-halides. ... 

Isomerically pure vinyl halides are important starting materials for preparation of the corresponding vinyl lithium species (see Section 7.1) and for use in Pd-catalyzed coupling reactions (see Section 7.10). Halogenation of vinylsilanes offers a valuable route for the synthesis of both (E)- and (Z)-vinyl halides. These reactions involve addition of the halogen to the double bond, followed by elimination of the silicon and halide moieties. The stereochemical outcome of the reaction will depend on both the mode of addition and the mode of elimination. For example, bromination of (Z)-vinylsilanes with bromine in CH2CI2 proceeds via an anti-addition. Treatment of the bromine adduct with sodium methoxide results in anti-desilicobromination. The conversion of the vinylsi-lane into the vinylbromide occurs with overall inversion of the double bond stereochemistry. " ... 

A similar conversion of cyclic vinyl halides or triflates 49 leads to carbocyclic or heterocyclic systems 50. ... 

The usefulness of nucleophile-promoted Iminium Ion-alkyne cyclizations derives from the ready availability of alkynylamines and the subsequent transformations of the cyclization products made possible because of their vinylic functionality (e.g., equations 1 and 2). Equation 2 illustrates use of this chemistry to elaborate an exocyclic tetrasubstituted double bond with complete stereooontrol. Net "reductive iminium ion alkyne cyclizations can be accomplished by dehalogenation of vinyl halide cyclization products. The conversion illustrated in equation 3 is a key step in an efficient, practical synthesis of the cardiotonic frog alkaloid pumiliotoxin A. ... 

As a reactive monomer forms a stable free radical, the radical reactivity will be the reverse order of the series given above. This means that monomers containing conjugated systems (styrene, butadiene, acrylates, acrylonitriles, etc.) will be highly reactive monomers but will form stable and so relatively unreactive radicals. Conversely, nonconjugated monomers (ethylene, vinyl halides, vinyl acetate, etc.) are relatively unreactive toward free radicals but will form unstable and highly reactive adducts. 

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