Organometallic compounds allene, reactions with

Reactions of allenes with halides are terminated by attack of organometallic compounds. The reaction of the 2-(2,3-butadienyl)iodobenzene (457) was terminated with alkenyl borane to give 458 [173]. 3-Methyl-1,2-butadiene (459) reacts with ary iodide, and the reaction is terminated by the attack of arylboronic acid 460 to afford 461 [174]. 

Indium-mediated allylation of trialkyl(difluoroacetyl)silane 70 in aqueous media gives homoallylic alcohol 71 exclusively (Scheme 60). Both water and THF are essential for the allylation reaction. It is worth noting that homoallylic alcohol 71 is formed exclusively under these reaction conditions. On the contrary, enol silyl ether 72 is a major product of the fluorinated acylsilanes reaction with other organometallic compounds than indium via a Brook rearrangement and defluorination. Indium-mediated allylsilylation of carbonyl compounds provides a facile route to 2-(hydroxyethyl)allylsilanes. The allene homologs are similarly prepared (Scheme 61).244,244a... 

The reactions between the imines and the allenic organometallic compounds give the three allylamines with very high stereoselectivity, while the reaction with 9-but-2-enyl-9-BBN gives the analogous erythro allylamines stereoselectivity (Scheme 12.1) [10]. 

More attractive copper-catalyzed (mediated) transformations of allenes into alkynes were reported by Caporusso and co-workers [27f, 73-75], Allenes 142 were converted into alkynes 143 by treatment with stoichiometric amounts of a cuprate species, as exemplified in Scheme 14.35. The problem of regioselective formation of either alkyne 143 or allene 144 was solved by the proper choice of the organometallic species. Preferential formation of alkynes 143 could be achieved employing cuprates such as R3Cu(CN)ZnCl-LiCl, which are prepared from organozinc compounds. On the other hand, reactions of organomagnesium derived cuprates (R3CuBr)Mg-LiBr mostly provided allenes 144 as major components. 

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