Allenes, halogenation rearrangement

Relatively few data and no systematic studies of the halogenation of dienes have been reported. Monoaddition products are usually formed through the attack on the more substituted double bond. Interhalogens add to allenes to give products in which the positive part of the reagent is attached to the central allenic carbon. Rearrangements, however, may affect product distributions. Ionic mechanisms are usually established, but very few details are available. 

Rearrangements are less likely when the allene to be formed is highly substituted with either phenoxy [23a], aryl, or halogen groups [23b, 24]. For example,... 

Allenes are generally prepared by elimination of halogens, hydrogen halides, or water from adjacent carbon atoms, the dehalogenation of gem-dihalocyclo-propanes, rearrangement of acetylenes, and the 1,4-addition to vinylacetylenes. 

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