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It Is Not Just Up to the Substrate: Palladium(0) Cyclizes Nazarov Substrates through Intramolecular Allylic Alkylation
Organometallics ( IF 2.5 ) Pub Date : 2017-09-13 00:00:00 , DOI: 10.1021/acs.organomet.7b00494
Tülay A. Ateşin 1 , Gabriela M. Martinez 1 , David Flores 1
Affiliation  

Plausible mechanisms of Pd0-catalyzed cyclization of diketoesters were modeled using density functional theory calculations. Comparison of the reaction mechanisms of uncatalyzed and Pd0-catalyzed cyclizations revealed the vital role of the Pd0 catalyst. Both reactions favor a stepwise mechanism involving a proton transfer followed by carbon–carbon bond formation over either the reverse order or a concerted mechanism. The key step for the Pd0-catalyzed reaction is the formation of a relatively stable intermediate, an η3-allyl PdII complex, in the lowest energy pathway. Our proposed mechanism is consistent with a Pd0-catalyzed intramolecular allylic alkylation reaction, previously referred to as “Nazarov-type” reactions. It is worth noting that, in contrast to many allylic alkylations, the Pd0-catalyzed cyclization does not require any additional reagents or an activated leaving group to form an η3-allyl PdII complex; thus, the α-hydroxycyclopentenone is produced from diketoesters with no waste. Furthermore, the asymmetric version of this reaction is the first known example of the use of an allylic alkylation reaction for the synthesis of a chiral cyclopentenone unit.

中文翻译:

它不仅取决于基质:钯(0)通过分子内烯丙基烷基化环化Nazarov基质

使用密度泛函理论计算对Pd 0催化二酮酸酯环化的合理机理进行了建模。比较未催化的和Pd 0催化的环化的反应机理,揭示了Pd 0催化剂的重要作用。这两个反应都有利于逐步的机制,涉及质子转移,然后形成碳-碳键,而不是相反的顺序或协调的机制。PD的关键步骤0 -催化的反应是一个相对稳定的形成中间,η 3 -烯丙基钯II复杂,在最低能量途径。我们提出的机制与Pd 0一致-催化的分子内烯丙基烷基化反应,以前称为“ Nazarov型”反应。值得注意的是,与许多烯丙基烷基化中,Pd 0 -催化的环化反应不需要任何额外的试剂或活化的离去基团以形成η 3 -烯丙基钯II复合物; 因此,α-羟基环戊烯酮是由二酮酯生产的,没有浪费。此外,该反应的不对称形式是使用烯丙基烷基化反应合成手性环戊烯酮单元的第一个已知实例。
更新日期:2017-09-14
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