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Insight into the origins of the reactivity and selectivity for the aminocatalytic [2+2] cycloaddition reaction
- Zhang, Beibei, Li, Yajie, Jiao, Mingyang, Ju, Yi-wen, Chen, Bo-Zhen
- Tetrahedron 2019 v.75 no.25 pp. 3421-3431
- catalysts, chemical structure, cycloaddition reactions, hydrogen bonding, organic compounds, regioselectivity, stereoselectivity
- A density functional study of the [2 + 2] cycloaddition between methyleneindolinones and enals catalyzed by prolinol derivatives is presented here. The calculations show that dienamines could be generated under acid-free conditions, and the hydroxyl of the catalysts plays a key role in the formation of dienamines. The following cycloaddition process between methyleneindolinones and the new formed dienamines includes two-step intramolecular electron transfers. The stereoselectivity is mainly attributed to the charge distributions on the reaction centers and the H-bonding interaction between the catalysts and methyleneindolinones. The excellent 3,4-regioselectivity is largely ascribed to the fact that the pre-product of 1,2-reactivity is tough to hydrolyze, but could return to the precursor. Besides, the large steric hindrance of catalysts is not conducive to the 3,4-reactivity, while the H-bonding between the catalysts and methyleneindolinones has less effect on the regioselectivity.