The Persistent Radical Effect: From Mechanistic Curiosity to Synthetic Tool

The Fischer–Ingold persistent radical effect (PRE) provides a simple conceptual framework to rationalize reactivities in systems involving two radicals with very different self‐reaction rate constants; in a limiting, but rather common case, one of these radicals is persistent at room temperature. In these cases, the cross‐coupling product is strongly favored. This contribution summarizes some of the work carried out at the University of Ottawa, where the PRE plays a key role in determining product distributions. Much of this work was inspired by the seminal contributions of Hanns Fischer.     

半群环为Bear—半单环的条件

讨论半群环 R[S]的 Bear-根 ,刻划了 R[S]是 Bear-半单环的充分和必要条件 .     

Minimizing Polynomials via Sum of Squares over the Gradient Ideal

A method is proposed for finding the global minimum of a multivariate polynomial via sum of squares (SOS) relaxation over its gradient variety. That variety consists of all points where the gradient is zero and it need not be finite. A polynomial which is nonnegative on its gradient variety is shown to be SOS modulo its gradient ideal, provided the gradient ideal is radical or the polynomial is strictly positive on the real gradient variety. This opens up the possibility of solving previously intractable polynomial optimization problems. The related problem of constrained minimization is also considered, and numerical examples are discussed. Experiments show that our method using the gradient variety outperforms prior SOS methods.     

自由基CH（X^2П，α^4∑^-）的光谱数据从头算研究

用分子轨道从头算方法，对CH自由基的基态（X^2П）和低激发态（α^4∑^-）的光谱数据进行了计算。计算结果表明，在基态CH（X^2П）时。在QCISD（T）／6-311G＋＋（3df．3pd）水平上．计算所得的键长R=0.1120981nm，偶极矩μ=1．5891 Debye，υ=2845．43cm^-1均与实验值相吻合，在B3PW91／6-311G＋＋（3df，3pd）理论水平上，计算的基态能量为-38．496143Hartree。误差仅为0．22％；对低激发态CH（α^4∑^-），使用含时的密度泛函方法（TDDPT）和大基组6—311＋＋G（3df，3pd）计算所得的R=0．1094nm，垂直跃迁能量为0．926eV，均与实验结果有较好的吻合。     

Synthesis of the cis diastereoisomer of 5-diethoxyphosphoryl-5-methyl-3-phenyl-1-pyrroline N-oxide (DEPMPPOc) and ESR study of its superoxide spin adduct

The cis and trans diastereoisomers of 5-diethoxyphosphoryl-5-methyl-3-phenyl-1-pyrroline N-oxide (DEPMPPO), the C(3)-phenyl analogue of DEPMPO, were prepared in three steps from phenylacetaldehyde and used in ESR-spin trapping of various carbon-, oxygen- and sulfur-centred radicals. In the case of the cis-isomer, the presence of the phenyl group cancels the alternating line width phenomenon observed for the DEPMPO-OOR (R = H, Bu^t) spin adducts. The ESR spectra of the DEPMPPOc-OOR spin adducts exhibit more straightforward patterns and are more easily assignable.     

Bu3SnH-mediated radical cyclisation onto azoles

Alkyl radicals have been cyclised onto pyrroles, imidazoles and pyrazoles, and acyl radicals cyclised onto pyrroles, using Bu₃SnH-, (TMS)₃SiH- and Bu₃GeH-mediated aromatic homolytic substitution for the synthesis of bicyclic N-heterocycles. The reactions yield intermediate π-radicals that lose hydrogen in the rearomatisation step of the aromatic homolytic substitution. Mechanistic studies of these rearomatisation steps indicate aromatic homolytic substitution in which the initiator or breakdown products from the inhibitor are responsible for the H-abstraction step.     

Jacobson Radicals Graded by G-sets

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(PCy3)2Cl2RuCHPh Catalyzed Kharasch additions. Application in a formal olefin carbonylation

(PCy₃)₂Cl₂RuCHPh-catalyzed Kharasch additions of trihaloalkanes across olefins provide polyhalogenated adducts, which upon hydrolysis furnish α,β-unsaturated ketones, aldehydes, or γ-hydroxybutenolides. This two-step process represents an overall acylation or carbonylation of an olefin.     

Selective synthesis, structure and oxidation properties of isomeric 1,4-dithiins fused to two benzo[b]thiophenes

Two novel isomers of 1,4-dithiins fused to two benzo[b]thiophenes on both sides were obtained by selective synthetic methods via the corresponding sulfides. The crystal structures of two dithiins were determined by X-ray crystallographic analyses. Examination of oxidation properties of the dithiins showed interesting results by CV measurement. The ESR spectra of chemically oxidized dithiins indicated formation of stable radical cations.     

Highly diastereoselective radical addition to glyoxylate imines of chiral amines without additional heteroatoms

The diastereoselective addition of alkyl radicals to glyoxylate imines of α-alkylbenzylamines has been investigated and it was found that diastereoselectivity improved as the size of the alkyl group increased.