Entropy Control of the Cross-Reaction between Carbon-Centered and Nitroxide Radicals
摘要:
Absolute rate constants for the cross-coupling reaction of several carbon-centered radicals with various nitroxides and their temperature dependence have been determined in liquids by kinetic absorption spectroscopy. The rate constants range from <2 x 10(5) M-1 s(-1) to 2.3 x 10(9) M-1 s(-1) and depend strongly on the structure of the nitroxide and the carbon-centered radical. Grossly, they decrease with increasing rate constant of the cleavage of the corresponding alkoxyamine. In many cases, the temperature dependence shows a non-Arrhenius behavior. A model assuming a short-lived intermediate that is hindered to form the coupling product by an unfavorable activation entropy leads to a satisfactory analytic description. However, the behavior is more likely due to a barrierless single-step reaction with a low exothermicity where the free energy of activation is dominated by a large negative entropy term.
A thermal O-to-C [1,3]-rearrangement of α-hydroxy acid derived enol ethers was achieved under mild conditions. The 2-aminothiophenol protection of carboxylic acids facilitates formation of the [1,3] precursor and its thermalrearrangement via stabilization of a radical intermediate. Experimental and theoretical evidence for dissociative radical pair formation, its captodative stability via aminothiophenol
Lewis Basic Salt-Promoted Organosilane Coupling Reactions with Aromatic Electrophiles
作者:Tyler W. Reidl、Jeffrey S. Bandar
DOI:10.1021/jacs.1c05764
日期:2021.8.11
Lewis basic saltspromote benzyltrimethylsilane coupling with (hetero)aryl nitriles, sulfones, and chlorides as a new route to 1,1-diarylalkanes. This method combines the substrate modularity and selectivity characteristic of cross-coupling with the practicality of a base-promoted protocol. In addition, a Lewis base strategy enables a complementary scope to existing methods, employs stable and easily
Visible Light-Induced Selective Generation of Radicals from Organoborates by Photoredox Catalysis
作者:Yusuke Yasu、Takashi Koike、Munetaka Akita
DOI:10.1002/adsc.201200588
日期:2012.12.14
A new strategy for the generation of carbon-centered radicals via oxidation of alkyl-, allyl-, benzyl- and arylborates by visible-light-driven single electron transfer (SET) photoredoxcatalysis has been established. The generated radicals smoothly react with TEMPO and electron-deficient alkenes to afford CO and CC coupling products, respectively. In this radical initiating system, cyclic organo(triol)borates
Reactions of the “Stable” Nitroxyl Radical TEMPO with Ketenes: Formation of a Unique Peroxidic Source of Aminyl Radicals
作者:Wen-wei Huang、Huda Henry-Riyad、Thomas T. Tidwell
DOI:10.1021/ja982944i
日期:1999.4.1
thermal decomposition of 6 show a 100-fold rate acceleration relative to (PhMe2CO)2. Thermal reactions of TEMPO with the bisketene (Me3SiCCO)2 (23) at 90 °C and with the allenylketene 26 also lead to deoxygenation of TEMPO, forming radicals 15, together with 2,3-bis(trimethylsilyl)maleic anhydride (24) and the alkylidenelactone 27, respectively.
B3LYP 水平的计算预测自由基 H2NO 添加到 CH2CO 的羰基碳上会放热 18.7 kcal/mol。与该预测一致,乙烯酮 Ph2CCO 在 25 °C 与四甲基哌啶基氧基 (TEMPO, TO) 反应生成不稳定物质,该物质与氧反应形成过氧化物 (OCPh2CO2T)2 (6, T = 2,2,6,6 -四甲基哌啶基),其结构已通过 X 射线晶体学证实。在 TEMPO 条件下,在 100 °C 的甲苯中加热 6 产生 Ph2CO、四甲基哌啶和 PhCH2OT,表明 6 分解形成两个 2,2,6,6-四甲基哌啶基自由基 15。6 的热分解动力学研究表明 100 -倍率加速相对于 (PhMe2CO)2。
The Formal Cross‐Coupling of Amines and Carboxylic Acids to Form sp
<sup>3</sup>
–sp
<sup>3</sup>
Carbon–Carbon Bonds
作者:Zirong Zhang、Tim Cernak
DOI:10.1002/anie.202112454
日期:2021.12.20
acid C−C coupling would be a valuable addition to the synthetic toolbox of carbon–carbon bond-formingreactions. Using miniaturized high-throughput experimentation, we have developed the first amine–acid cross-coupling to form C(sp3)−C(sp3) bonds based on preactivation of the building blocks and nickelcatalysis.