Radical addition halo-olefins

Carbamates. Lower alkyl A/-halo- and W,W-dihalocarbamates are distillable Hquids (70,112). A/-Halo-A/-metallocarbamates are crystalline hygroscopic soHds. A/-Chloro-A/-sodiourethane [17510-52-0] C2H OCONQNa, does not decompose on heating to 250°C (113), but violent decompositions have occurred at room temperature (114). A/-Halocarbamates react with a variety of organic substrates, eg, the free-radical addition of W-chlorourethane [16844-21 -6] C2H OCONHCl, and A,A-dichlorourethane [15698-16-5], C2H OCONCl2, to olefins provides a convenient route to... 

For olefins with Ji-substitucnts, whether electron-withdrawing or electron-donating, both the HOMO and LUMO have the higher coefficient 021 the carbon atom remote from the substituent. A predominance of tail addition is expected as a consequence. However, for non-conjugated substituents, or those with lone pairs (e.g. the halo-olefins), the HOMO and LUMO are polarized in opposite directions. This may result in head addition being preferred in the case of a nucleophilic radical interacting with such an olefin. Thus, the data for attack of alkyl and fluoroalkyl radicals on the fluoro-olefins (Table 1.2) have been rationalized in terms of FMO theory.16 Where the radical and olefin both have near neutral philicity, the situation is less clear.21... 

The groups R2N and Cl can be added directly to olefins, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-N-chloroamines and acids.663 These are free-radical additions, with initial attack by the R2NH + radical ion,664 N-Halo amides RCONHX add RCONH and X to double bonds under the influence of uv light or chromous chloride.665 For an indirect way of adding NH2 and I to a double bond, see 5-32. 

Several variations of this reaction are possible. The halo acid is boiled with a solution of sodium in absolute alcohol as in the formation of y-bu-tyrolactone (67%), or the dry sodium salt of a halo acid is heated under vacuum as in the preparation of 8-valerolactone (30%). The corresponding esters are sometimes refluxed with alcoholic potassium hydroxide or decomposed thermally at 15 180° whereby a molecule of an alkyl halide is eliminated. The latter process is valuable in making a-alkyl-y-lac-tones of higher-molecular-weight acids since the y-bromo esters are available by the free-radical addition of a-bromo esters to 1-olefins. 

The methods described thus far represent only a small subset of the available methodologies for the formation of C-furanosides and C-pyranosides. Other methods shown to be useful include cyclizations of halo olefins and ene-ynes. As shown in Scheme 7.6.1, Lee, et al.,29 prepared halo olefins from suitable alcohols and acetylenic esters. Subsequent application of free radical conditions thus effected cyclizations. All reactions proceeded in yields exceeding 95%. Furthermore, where the formation of diastereomers was an issue, selective cis formation was observed. Thus the ease of preparation of the vinyl ether substrates required for these cyclization reactions makes this methodology an extremely useful addition to the technology surrounding the preparation of C-glycosides. 

A variety of atom transfer radical reactions involving addition of halo, phenyl-seleno, and phenylthio sulfonates have been developed. In these reactions, it is believed that the sulfonyl radical attacks the olefin, and the halogen or arylchalcogen... 

Radical addition of halo methanes to olefins was achieved by Kharasch and his co-workers98,99 when they warmed a mixture of an olefin with, e.g., carbon tetrabromide or an excess of carbon tetrachloride in the presence of 1-5 mole % of a diacyl peroxide at 70-90° ... 

Munoz-MoHna JM, Belderrain TR, Perez PJ. An efficient, selective, and reducing agent-free copper catalyst for the atom-transfer radical addition of halo compounds to activated olefins. Inorg Chem. 2010 49 642-645. 

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