Phosphine-catalyzed [4 + 2] annulation and vinylogous addition reactions between 1,4-dien-3-ones and 1,1-dicyanoalkenes |
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Authors: | Zhou Rong Wang Jianfang Tian Junjun He Zhengjie |
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Institution: | The State Key Laboratory of Elemento-Organic Chemistry and Department of Chemistry, Nankai University, Tianjin, China. |
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Abstract: | Phosphine-catalyzed 4 + 2] annulation and vinylogous Michael addition reactions between 1,4-dien-3-ones and 1,1-dicyanoalkenes are presented. Under the catalysis of PBu(3) (20 mol %), 1,4-dien-3-ones like styryl ketones with 2-aryl 1,1-dicyanoalkenes as doubly activated alkenes readily undergo a formal 4 + 2] cycloaddition reaction, affording polysubstituted cyclohexanones in satisfactory yield and good diastereoselectivity; with the doubly activated alkenes bearing an acidic methyl or methylene at the 2-position, a vinylogous Michael addition of 1,4-dien-3-ones occurs under the same reaction conditions, giving a non-cyclized multifunctional adduct in good yield. These two phosphine-catalyzed transformations represent atom economical carbon-carbon bond forming reactions capable of rapid construction of molecular complexity. Based on experimental results, formation of the products has been mechanistically rationalized, and a phosphonium activation is proposed. |
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