Rh-Catalyzed Cycloisomerization of 1,7-Ene-Dienes to Synthesize trans-Divinylpiperidines: A Formal Intramolecular Addition Reaction of Allylic C-H Bond into Dienes.

An originally designed Rh-catalyzed [4 + 2] cycloaddition reaction of nitrogen-tethered 1,7-ene-dienes turned out to be a cycloisomerization reaction, which involves allylic C-H activation/alkene insertion into Rh-H bond/reductive elimination processes. Deuterium labeling experiments gave support to the proposed mechanism. This unexpected cycloisomerization reaction provides an efficient way to synthesize trans-divinylpiperidines from easily accessed linear 1,7-ene-dienes.