Radical cyclization in heterocycle synthesis 15. Relationship between a Radical species and radical acceptors of three different types of double bond in radical addition-cyclization |
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Authors: | Miyata Okiko Kajisa Seiko Ueda Masafumi Yamauchi Masashige Naito Takeaki |
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Institution: | Kobe Pharmaceutical University, Motoyamakita, Higashinada, Kobe 658-8558, Japan. |
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Abstract: | Relationship between a radical species and radical acceptors of three different types of double bond in radical addition-cyclization was systematically investigated. Substrates carrying alpha,beta-unsaturated amide, isolated olefin, and oxime ether moieties underwent radical addition-cyclization to give differently substituted lactams depending upon the radicals used. The sulfanyl radical addition-cyclization of the substrate proceeded smoothly to give the 5-membered lactam having an alkoxyamino group as a result of preferable addition of an intermediary alpha-carbonyl radical to the oxime ether. On the other hand, the triethylborane-mediated radical addition-cyclization gave the lactam bearing an iodomethyl group as a result of addition to an intermediary alpha-carbonyl radical to isolated olefin. The different regioselectivity was explained by the stability of the intermediary radical and the interaction between SOMO and HOMO. |
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