Migratory Aptitudes in Rearrangements of Destabilized Vinyl Cations
Migratory Aptitudes in Rearrangements of Destabilized Vinyl Cations
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不稳定乙烯基阳离子重排的迁移能力
DOI：
10.1021/acs.joc.9b02130
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发表时间：
2019-12-06
影响因子：
3.6
通讯作者：
Brewer, Matthias
中科院分区：
文献类型：
--
作者：
Cleary, Sarah E.;Hensinger, Magenta J.;Brewer, Matthias
刘易斯酸促进β-羟基重氮酮生成不稳定的乙烯基阳离子，导致能量上有利的1，2-移位穿过烯烃，随后是不可逆的C-H插入，得到环戊烯酮产物。该反应序列克服了乙烯基阳离子的反离子捕获和重排可逆性的典型挑战，并已被用于研究不常见的C（sp（2））到C（sp）乙烯基阳离子重排中的非等价取代基的迁移倾向。迁移倾向的趋势与其他阳离子重排中观察到的一致;可以最好地稳定阳离子的取代基更容易迁移。然而，密度泛函理论计算表明，情况更为复杂。乙烯基阳离子的一种构象异构体的形成的选择性和由于乙烯基阳离子与相邻羰基氧之间的静电相互作用而导致的跨烯烃的面选择性迁移协同工作以确定哪个基团迁移。这项研究提供了有价值的洞察力预测迁移偏好时，应用这种方法来合成结构复杂的环戊烯酮，差异取代的α和β位置。
The Lewis acid-promoted generation of destabilized vinyl cations from beta-hydroxy diazo ketones leads to an energetically favorable 1,2-shift across the alkene followed by an irreversible C-H insertion to give cyclopentenone products. This reaction sequence overcomes typical challenges of counter-ion trapping and rearrangement reversibility of vinyl cations and has been used to study the migratory aptitudes of nonequivalent substituents in an uncommon C(sp(2)) to C(sp) vinyl cation rearrangement. The migratory aptitude trends were consistent with those observed in other cationic rearrangements; the substituent that can best stabilize a cation more readily migrates. However, density functional theory calculations show that the situation is more complex. Selectivity in the formation of one conformational isomer of the vinyl cation and facial selective migration across the alkene due to an electrostatic interaction between the vinyl cation and the adjacent carbonyl oxygen work in concert to determine which group migrates. This study provides valuable insight into predicting migration preferences when applying this methodology to the synthesis of structurally complex cyclopentenones that are differentially substituted at the alpha and beta positions.