Reactive ketimino radical acceptors: intermolecular alkyl radical addition to imines with a phenolic hydroxyl group |
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Authors: | Miyabe Hideto Yamaoka Yousuke Takemoto Yoshiji |
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Affiliation: | Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. |
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Abstract: | Intermolecular carbon radical addition to the carbon-nitrogen double bond of ketimines was studied. In the study on the reactivity of various aldimines, we found that the aldimine 7 having a phenolic hydroxyl group shows an excellent reactivity toward nucleophilic carbon radicals. A remarkable effect of phenolic hydroxyl group is assumed to be the stabilization of intermediate aminyl radical provided by a hydroxyl group. The screening of reactive ketimino acceptors showed that ketimines 15, 17, and 19 having a phenolic hydroxyl group exhibit excellent reactivities. The radical addition to ketimines 15, 17, and 19 took place regioselectively at the imino carbon to give the C-alkylated products without the formation of N-alkylated products. Enantioselective ethyl radical addition to ketimine 15 using chiral box ligand and Zn(OTf)2 gave the diethylated product 30 in 80% ee. |
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