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Free Radical-mediated Ring Expansion Reactions:Endocyclic Cleavage of Cyclopropylcarbinyl Radicals
이필호,이병철,이구연,이창희,장숙복,Lee, Pil Ho,Lee, Byeong Cheol,Lee, Gu Yeon,Lee, Chang Hui,Jang, Suk Bok Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.6
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.