Round trip radical reactions

The third, less common, round trip radical reaction process starts at one end of the chain and works its way back to the same end [79]. 

Scheme 3.52. Improved "round trip radical reaction" for the synthesis of linear fused [5.5.5]tricycles.

Haney, B.P., and Curran, D.P., Round trip radical reactions from acyclic precursors to tricy-clo[5.3.1.0 - ]undecanes. A new cascade radical cyclization approach to ( )-isogymnomitrene and ( )-gymnomitrene, J. Org. Chem., 65, 2007, 2000. 

A dramatic improvement in this new round trip radical domino processes developed by Curran s group was presented by Takasu, Ihara and coworkers. The new method relies on the introduction of a conjugated ester moiety at the terminal olefm, thereby effecting an acceleration of the domino reaction accompanied with an enhancement of the regio- and stereoselectivity [81]. Thus, reaction of 3-196 with Bu3SnH led to a 4 3 mixture of the two diastereomeric tricycles 3-197 and 3-198 in 83% yield. In this process, the vinyl radical 3-199 is initially formed, but this smoothly cyclizes in 5-exo-trig manner to give radical 3-200 (Scheme 3.52). Due to... 

---