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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 6
BKCSDE 21(6)
June 20, 2000 

Free Radical-Mediated Ring Expansion Reactions: Endocyclic Cleavage of Cyclopropylcarbinyl Radicals
Phil Ho Lee, Byungcheol Lee, Kooyeon Lee, Chang-Hee Lee, Sukbok Chang
Ring expansion reactions via endocyclic cleavage of cyclopropylcarbinyl radicals derived from the reaction of [1-benzyloxycarbonylbicyclo[n. 1.O]alk-(n+l)-yl] -1-imidazolethiocarboxylates with tributyltin hydride/AIBN proceeded to produce 3-cycloalkenecarboxylates in good yields. Benzyl (5'-phenoxypentyl) -3-cyclohepten-1 -carboxylate was obtained in 33% yield from the reaction of benzyl 5-methylenebicyclo [4. 1.0]- 1-carboxylates with 4-phenoxybutyl iodide under radical conditions. Selective cleavage of endocyclic bond in cyclopropane to the cyclohexane, results from stabilization of the resultant radical by the carbonyl groups, such as the benzyloxycarbonyl group, which lower the transition state energy for the final cyclopropane cleavage in the ring expansion.
595 - 603
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