Selenols radical additions

Radical Addition of Selenols and Diselenides to Alkynes and Allenes... 

Pd(OAc)2-catalyzed hydroselenation of alkynes with PhSeH can be applied to the hydroselenation of allenes (Scheme 15.83). Whereas radical addition of selenols to allenes leads to fhe formation of regioisomeric mixtures of vinylic selenides [145], the Pd(OAc)2-catalyzed hydroselenation provides the corresponding vinylic selenides with moderate to high regioselectivity [163]. 

They also revealed that primary alkyl-, vinyl-, and aryl-substituted acy radicals generated by treating selenol esters with Bu3SnH can be utilized in intermole-cular alkene addition reactions (Eq. 48) [99,98b]. Acyl radicals exhibit nucleophilic character and react efficiently with alkenes bearing electron-withdrawing or radical-stabilizing groups. 

In 1992 Ogawa, Sonoda et al. carried out the first catalytic addition of aromatic thiols [143] and selenols [144] to alkynes with Pd(OAc)2. Although the Markovnikov isomer was the major product of the reactions, the yields were not very high [145]. The catalytic reaction was accompanied with non-catalytic addition, leading to the anti-Markovnikov isomers (free radical or nucleophilic reactions) as well as double bond isomerization in the case of thiols (TH F, 67 °C) and selenols (benzene, 80 °C) [143, 144]. The isomerization reaction was especially pronounced with Pd(PhCN)2Cl2 catalyst [146]. It is interesting to note that the intermediate metal complex taking part in the catalytic reaction was denoted as Pd(SPh)2L [146]. 

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