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Stereoelectronic constraints in the aryl radical cylization of phenethylenamides
Tetrahedron Letters ( IF 1.8 ) Pub Date : 2020-03-30 , DOI: 10.1016/j.tetlet.2020.151871
Armando Navarro-Vázquez , Domingo Domínguez

The 7-endo-trig and 6-exo-trig cyclizations of the N-formylphenethylenamide radicals have been computationally studied at the UM062X/6-31+G** and UPW6B95-D3 DFT levels of theory. Computations show a regioselectivity preference for the 7-endo process over the 6-exo in agreement with known experimental results. This 7-endo process takes place preferentially through a transition structure of half-boat geometry which fully retains enamide planarity. On the other hand, the 6-exo-trig cyclization prefers a chair transition structure geometry which places the N-vinyl group in a pseudo-equatorial position. Computations also show that conformational locking in cyclic enamides greatly increases the preference for the 7-endo path in agreement with experimentally observed outcomes.



中文翻译:

苯乙酰胺的芳基自由基环化中的立体电子约束

已在理论上以UM062X / 6-31 + G **和UPW6B95-D3 DFT进行了N-甲酰基苯乙酰胺基的7--trig和6- exo- trig环化的研究。计算表明,与已知的实验结果相一致,7-内切过程对区域选择性高于6- exo。该7-过程优选地通过半船形几何结构的过渡结构来进行,该过渡结构完全保持酰胺平面度。另一方面,6- exo- trig环化更喜欢将N-乙烯基位于伪赤道位置。计算还表明,环酰胺中的构象锁定大大增加了对7-内径途径的偏好,与实验观察到的结果一致。

更新日期:2020-03-30
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