A novel and highly efficient two-carbon ring expansion.
[reaction: see text]. Dynamic gas-phase thermoisomerization (DGPTI) of medium- and large-ring 3-vinylcycloalkanones at 600-630 degrees C produces isomeric gamma,delta-unsaturated cycloalkanones expanded by two carbon atoms. A reaction mechanism involving an open-chain diradical intermediate, followed by intramolecular recombination under insertion of the vinyl group is proposed. Substituents on the vinyl moiety are transferred locospecifically to the ring-expanded ketones as corresponding beta- and gamma-substituents, respectively. The preparation of extraordinary cyclic allenes can be accomplished by DGPTI (540 degrees C) of 3-ethinylcyclododecanone.
Organisch-Chemisches Institut der Universität, 8057 Zürich, Switzerland. georg@access.unizh.ch
Georg
G
Rüedi
Matthias
M
Nagel
Hans-Jürgen
HJ
Hansen