Electron Transfer Photochemistry of Homochrysanthemol: Intramolecular Nucleophilic Attack on the Cyclopropane Ring.
The electron-transfer photochemistry of homochrysanthemol, 1, resulted exclusively in intramolecular "substitution" at the quaternary cyclopropane carbon, generating the five-membered cyclic ethers, 2 and 4. The alternative "addition" to the terminal carbon of the double bond, which would result in seven-membered cyclic ethers, 3 and 5, was not observed. Apparently, the five-membered transition state leading to 2 and 4 is significantly favored over the seven-membered one required for formation of 3 and 5. These results stand in interesting contrast to the previously established reaction pattern of chrysanthemol, 8, which is captured exclusively at the terminal vinyl carbon. The divergent regiochemistry of 1(*)(+) and 8(*)(+) (even though the tethers between vinylcyclopropane and alcohol functions differ only by a single CH(2) group) elucidates the principles governing the course of nucleophilic capture in radical cations.
Herbertz
Torsten
T
Department of Chemistry, Rutgers University, Wright-Rieman Laboratories, New Brunswick, New Jersey 08854-8087.
Roth
Heinz D.
HD