Barton esters alternative reactions

An excellent alternative to the classical Hunsdiecker reaction and its variants, which totally avoids the use of heavy metal salts and potent electrophilic reagents, consists of the simple photolysis or thermolysis of Barton esters in refluxing bromotri-chloromethane for the bromides or tetrachloromethane for the chlorides [4], The analogous decarboxylative iodination can also be achieved using iodoform as the reagent in a benzene/cyclohexene solvent system (Scheme 5). For the cases of vinylic and aromatic acids, where the usual problems of chain efficiency are encountered, the addition of azobisisobutyronitrile (AIBN) is also required [10]. Nevertheless, since this method can operate on both electron-rich and electron-poor aromatic systems, and moreover does not suffer from the competitive electrophilic aromatic bromination found with electron rich aromatics under normal Hunsdiecker conditions, this route to synthetically useful aryl iodides and bromides should find widespread application. 

N-0 bond cleavage of the Barton ester can also occur spontaneously upon heating or by irradiation with light to initiate the reaction. In this case, a radical initiator is not required but a hydrogen-atom (H-atom) donor is still necessary to form the RH. Alternative H-atom donors to tri- -butyltin hydride include tertiary thiols and organosilanes. 

J. Nicholas Kirwan, B. P. Roberts, and C. R. Willis, Deoxygenation of alcohols by the reactions of their xanthate esters with triethylsilane An alternative to tributyltin hydride in the Barton-McCombie reaction, Tetrahedron Lett., 31 (1990) 5093-5096. 

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