通过钯催化的C(sp 3)–C(sp 3)氢解对苄基的季碳,叔碳和仲碳中心进行修饰)呈现σ键。当在温和的氢解条件下(含钯碳和氢气的大气压)处理带有季苄基中心的苄基麦德鲁姆的酸衍生物时,就可以很好地获得高收率的芳族化合物,这些芳族化合物被叔苄基中心和麦德鲁姆酸所取代。类似地,含有叔或仲苄基中心的底物分别产生被仲苄基中心或甲苯衍生物取代的芳族化合物。此外,该策略用于二芳基甲烷的高产率合成。探索了还原性脱烷基反应的范围,并确定了对空间和电子因素的限制。描述了该反应的机理分析,该分析由氘标记实验和对映体富集的衍生物的氢解组成。调查显示,C(sp 3)–C(sp 3)σ键断裂事件是通过混合的S N 1 / S N 2机理发生的,其中钯中心置换了一个基于碳的离去基团,即Meldrum酸,其构型反转,随后通过还原消除钯来提供CH键。
Carbon-Based Leaving Group in Substitution Reactions: Functionalization of sp<sup>3</sup>-Hybridized Quaternary and Tertiary Benzylic Carbon Centers
作者:Stuart J. Mahoney、Tiantong Lou、Ganna Bondarenko、Eric Fillion
DOI:10.1021/ol301442z
日期:2012.7.6
Lewis acid promoted substitution reactions employing Meldrum’s acid and 5-methyl Meldrum’s acid as carbon-based leavinggroups are described which transform unstrained quaternary and tertiary benzylic Csp3–Csp3 bonds into Csp3–X bonds (X = C, H, N). Importantly, this reaction has a broad scope in terms of both suitable substrates and nucleophiles with good to excellent yields obtained (typically >90%)
reductive dealkylation reaction is explored and the limitations with respect to steric and electronic factors are determined. A mechanistic analysis of the reaction is described that consisted of deuterium labelling experiments and hydrogenolysis of enantioenriched derivatives. The investigation shows that the C(sp3)–C(sp3) σ bond‐cleaving events occur through a hybrid SN1/SN2 mechanism, in which the palladium
通过钯催化的C(sp 3)–C(sp 3)氢解对苄基的季碳,叔碳和仲碳中心进行修饰)呈现σ键。当在温和的氢解条件下(含钯碳和氢气的大气压)处理带有季苄基中心的苄基麦德鲁姆的酸衍生物时,就可以很好地获得高收率的芳族化合物,这些芳族化合物被叔苄基中心和麦德鲁姆酸所取代。类似地,含有叔或仲苄基中心的底物分别产生被仲苄基中心或甲苯衍生物取代的芳族化合物。此外,该策略用于二芳基甲烷的高产率合成。探索了还原性脱烷基反应的范围,并确定了对空间和电子因素的限制。描述了该反应的机理分析,该分析由氘标记实验和对映体富集的衍生物的氢解组成。调查显示,C(sp 3)–C(sp 3)σ键断裂事件是通过混合的S N 1 / S N 2机理发生的,其中钯中心置换了一个基于碳的离去基团,即Meldrum酸,其构型反转,随后通过还原消除钯来提供CH键。
Probing Persistent Intramolecular C−H···X (X = O, S, Br, Cl, and F) Bonding in Solution Using Benzyl Meldrum’s Acid Derivatives
作者:Eric Fillion、Ashraf Wilsily、Dan Fishlock
DOI:10.1021/jo802311w
日期:2009.2.6
Persistent intramolecular interactions between acidic C−H hydrogens and a variety of acceptors (X) (X = O, S, Br, Cl, and F) in solution were probed by 1H NMR experiments, using 5-benzyl Meldrum’s acid derivatives. To bring about formation of intramolecular C−H···X bonding, ortho-substituted benzyl Meldrum’s acids were designed, for which hydrogenbonding occurred through a six-membered ring. Introduction
酸性CHH氢与溶液中各种受体(X)(X = O,S,Br,Cl和F)之间的持久分子内相互作用通过1 H NMR实验使用5-苄基Meldrum的酸衍生物进行探测。为了形成分子内CH键·X键,设计了邻位取代的苄基麦德鲁姆酸,通过六元环进行氢键键合。在芳族部分上和在系链中引入取代基允许电子和空间因素的变化。麦德鲁姆酸的优越酸度影响了CH氢参与非经典CH-··X键的能力,并结合了空间位阻因子A 1,3,推动了苄基麦德鲁姆酸的构象性质。-烯丙基菌株。通过表征固态的苄基麦德鲁姆酸,通过X射线分析以及与溶液中观察到的相关构象,可以进一步了解分子内C-H···X键。