On the 6-exo atom transfer radical cyclization reactions of 3-butenyl 2-iodoalkanoates |
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Authors: | Fang Xingang Xia Hairong Yu Hui Dong Xicheng Chen Minbo Wang Quanrui Tao Fenggang Li Chaozhong |
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Institution: | Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China. clig@pub.sioc.ac.cn |
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Abstract: | Bis(tributyltin)-initiated atom transfer cyclization reactions of 3-butenyl iodoalkanoates in the presence of BF3.OEt2 as the catalyst afforded the 6-exo cyclization products as a mixture of 3,4-cis- and trans-substituted tetrahydro-2H-pyran-2-ones in 53-71% yield with the major isomers being the cis ones. Ab initio calculations at the B3LYP/6-31G level on the transition states of the radical cyclization and on the cyclized products revealed that the reactions are kinetically controlled and the transition states for the 6-exo radical cyclization are in boat conformations. Moreover, the cis-oriented transition states are of lower energy than the corresponding trans-oriented ones, which are in excellent agreement with experimental results. |
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