Allyl bromide Allyltributyltin

The most well-known radical allylation reagent is allyltributyltin. Typical radical allylations are carried out by the irradiation of a benzene solution of alkyl bromide or selenide and allyltributyltin in the presence of AIBN with a mercury lamp. Eqs. 4.32a and 4.32b show the allylation of a-bromosulfone (76) and a-phenylselenyl-cyclopentanone... 

Allyltributyltin (5) is the most commonly used reagent for carrying out allylation reactions via a free radical fragmentation process [5]. Keck reported the first practical use of allyltributyltin for free radical allylation reactions in 1982 in the context of a synthesis of perhydrohistrionicotoxin [6]. Heating bromide 4 with allyltributyltin in the presence of AIBN as a radical initiator gave the allylated derivative 6 (Scheme 3) in high yield with complete control of stereochemistry. Similar transformations had proven to be very difficult by standard ionic reactions. 

Further investigation by Keck of the scope of allylation reactions with allyltributyltin revealed that the reaction could be carried out with numerous different types of radicals, for example simple alkyl radicals, aryl radicals and radicals a to the oxygen atoms of ethers and esters [7]. These radicals were generated from several types of free radical precursors, such as bromides, iodides, phenylselenides,... 

Radical reactions have been further utilised in the construction of branched-chain sugars. Unsaturated iodide (24) with allyltributyltin or Bu3SnH and methyl acrylate has afforded the doubly-branched derivatives (25) and (26) by way of intra- and then inter-molecular radical processes. Similarly, bromide (27) gave the 3-C-allyl derivative (28) which, after transformation into enal (29), underwent a further radical cyclisation (Scheme... 

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