Cascade Reactions Initiated by Addition of S-Centered Radicals to Alkynes

1 Cascade Reactions Initiated by Addition of S-Centered Radicals to Alkynes 

The apparent chemoselectivity for the addition of the electrophilic S-centered radicals to the less electron-rich alkyne moiety in enyne 138 can be rationalized by the fact that addition of S radicals to both aUcenes and alkynes proceeds smoothly (the rate constants for addition of S radicals to alkenes are about three orders of magnitude larger than those for the addition to alkynes), but is also reversible. However, the reversibility is less pronounced for the radical addition to alkynes, due to the high reactivity of the vinyl radicals formed (compared to alkyl radicals), which undergo subsequent reactions at faster rates than undergoing fragmentation back to the S 

An interesting four-component radical cascade that leads to formation of 3-arylthio-substituted acrylamides 172 and involves thiyl radicals, aromatic acetylenes, and 

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