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35.2.1.8.5.1 Variation 1: Using Hydrogen Bromide and a Radical Source

DOI: 10.1055/sos-SD-035-00350

Roy, K.-M.Science of Synthesis, (200735367.

Information relating to the free-radical addition of hydrogen bromide to C=C bonds has been published,[‌5‌] and can also be found in HoubenWeyl, Vol.5/4, pp102119. The reaction is promoted by radical initiators such as UV radiation (light), oxygen (air), and various peroxides. Hydrobrominations of volatile alkenes are carried out in the gas phase, whereas higher alkenes are reacted in refluxing pentane, hexane, or heptane. As shown by numerous examples, radical addition of hydrogen bromide to terminal alkenes gives predominantly 1-bromoalkanes via anti-Markovnikov addition.[‌5‌] By contrast, hydrobromination of internal double bonds often leads to the formation of mixtures of isomeric bromides, as shown for the reaction of 2-methylbut-2-ene (Scheme 13).[‌5‌,‌27‌]

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