Bromination, allylic

Before we start, we recall (from equation (6.13)) that the magnitude of the CV current peak is proportional to concentration. Allyl alcohol and brominated allyl alcohol are not electroactive at all, so the CV only monitors the relative amount of bromine and bromide. The forward peak of the CV has a magnitude pa (where pa = peak, anodic ), and Ip<, a [bromide], becau.se bromide is converted at the peak to form bromine. 

Polymer Structure Modification. Chemical modification of the polymer structure includes the use of tetrahalophthalic acids or anhydrides, diallylphenyl phosphonate, brominated allyl phosphates, chlorendic anhydride, and tetrakishydroxymethyl phosphonium chloride. 

Burton, S. C., and Harding, D. R. K. (1997). High-density ligand attachment to brominated allyl matrices and application to mixed mode chromatography of chymosyn. J. Chromatogr. 775, 39-50. 

A modification called tandem [2,3] sigmatropic rearrangement of sulfonium ylide—bromine allylic rearrangement has been reported (88JOC5149). Thus, reaction of the C5 brominated 2-pyrone 224 with ethyl diazoacetate under rhodium catalysis results not only in transfer of the ester moiety to C5, as described earlier, but also in the transfer of the bromine atom from C5 to the side chain at C6 in such a way that the functional group remaining at that side chain, as in 225, can be further elaborated (89JHC1205). 

The advantage to using NBS to brominate allylic positions is that neither Br2 or HBr is formed at a high enough concentration to add to the double bond. 

AT-Bromosuccinimide (NBS) is frequently used to brominate allylic carbons because it allows a radical substitution reaction to be carried out in the presence of a low concentration of Br2 and a low concentration of HBr. If a high concentration is present, addition of Bt2 or HBr to the double bond will compete with allylic substitution. 

A racemic mixture is also obtained if a hydrogen bonded to an asymmetric center is substituted by a halogen. A-Bromosuccinimide (NBS) is used to brominate allylic carbons. 

Certain brominated allylic alcohols suffer loss of the elements of HBr when exposed to Heck-t)q)e reaction conditions and so affording the corresponding a, 8-unsaturated aldehydes or ketones (eq 121). ... 

The carboranyl Grignards do not appear to be as generally useful as the lithium derivatives in that they do not react with aldehydes or ketones 334). However, reported reactions with bromine, allyl bromide, or water proceed as might be expected 327, 334). 

The photocychzation of the Diels-Alder e do-adducts of cyclic dienes with p-benzoquinone has been successfully applied to the construction of polycyclic cages. Nair et al. reported that the photocychzation of the 2,5-bis(bromomethyl) compound 47 gave the unexpected cage compound 49 as a major product along with the anticipated product 48 (Scheme 9)." The formation of 49 can be explained through the initial photolytic cleavage of the bromine-allylic carbon bond (50) followed by radical reorganization and final bromine radical capture. 

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