Heterolytic and Homolytic N-NO Bond Dissociation Energies of N-Nitroso-benzenesulfonylmethylamines in Acetonitrile

Great interests have been accumulated in recent years in the chemistry and biochemistry of nitric oxide (NO) since the remarkable discoveries of its key roles in a wide range of human physiological processes. To elucidate the mechanistic details of NO migration from its donor to its acceptor, it is necessary to determine the Y-NO bind energy that registers the thermodynamic driving force for NO release and capture. In this paper the heterolytic and homolytic N-NO bond dissociation energies [ i. e., △Hhet(N-NO) and △Hhomo(N-NO)] for ten N-nitroso-p-substituted-benzensulfonyl methylamines in acetonitrile are offered, which were obtained from titration calorimetry and thermodynamic cycles, respectively (Scheme 1).     

An Environmentally Benign System for Synthesis of β-Hydroxylketones： L-Histidine Asymmetrically Catalyzed Direct Aldol Reactions in Aqueous Micelle and Water-like Media

The first histidine catalyzed direct aldol reactions of ketones with nitrobenzaldehydes in water and in poly（ethylene glycol） （PEG） were reported. It reveals that histidine is a good aldol catalyst for synthesis of β-hydroxylketones in water and in PEG, giving good to excellent yields of the respective products. Better enantioand regioselectivity were achieved using low molecular weight PEG as the media. The results show that histidine and PEG-200 or -300 may constitute a promising environmentally benign system for asymmetric synthesis of β-hydroxylketones.     

Thermodynamics and kinetics of the hydride-transfer cycles for 1-aryl-1,4-dihydronicotinamide and its 1,2-dihydroisomer

Five 1-(p-substituted phenyl)-1,4-dihydronicotinamides (GPNAH-1,4-H(2)) and five 1-(p-substituted phenyl)-1,2-dihydronicotinamides (GPNAH-1,2-H(2)) were synthesized, which were used to mimic NAD(P)H coenzyme and its 1,2-dihydroisomer reductions, respectively. When the 1,4-dihydropyridine (GPNAH-1,4-H(2)) and the 1,2-dihydroisomer (GPNAH-1,2-H(2)) were treated with p-trifluoromethylbenzylidenemalononitrile (S) as a hydride acceptor, both reactions gave the same products: pyridinium derivative (GPNA(+)) and carbanion SH(-) by a hydride one-step transfer. Thermodynamic analysis on the two reactions shows that the hydride transfer from the 1,2-dihydropyridine is much more favorable than the hydride transfer from the corresponding 1,4-dihydroisomer, but the kinetic examination displays that the former reaction is remarkably slower than the latter reaction, which is mainly due to much more negative activation entropy for the former reaction. When the formed pyridinium derivative (GPNA(+)) was treated with SH(-), the major reduced product was the corresponding 1,4-dihydropyridine along with a trace of the 1,2-dihydroisomer. Thermodynamic and kinetic analyses on the hydride transfer from SH(-) to GPNA(+) all suggest that the 4-position on the pyridinium ring in GPNA(+) is much easier to accept the hydride than the 2-position, which indicates that when the 1,4-dihydropyridine is used the hydride donor to react with S, the formed pyridinium derivative GPNA(+) may return to the 1,4-dihydropyridine by a hydride transfer cycle; but when the 1,2-dihydropyridine is used as the hydride donor, the formed pyridinium derivative can not return to the 1,2-dihydropyridine by the hydride reverse transfer from SH(-) to GPNA(+). These results clearly show that the hydride-transfer cycle is favorable for the 1,4-dihydronicotinamides, but unfavorable for the corresponding 1,2-dihydroisomers.     

BNAH还原质子化N—芳基芴亚胺反应的热力学及机理研究

利用热力学循环方法，通过ｐＫ和有关电化学数据的测定，首次得到了ＮＡＤ（Ｐ）Ｈ的辅酶模型物（ＢＮＡＨ）按不机理还原质子化Ｎ－芳基芴亚胺的各基元步骤的自由能变化，结合得到的同位素标纪结果，从热力学趋动力的角度区分了氢负离子的转移机理。     

A detailed investigation of subsitituent effects on N-h bond enthalpies in aniline derivatives and on the stability of corresponding N-centered radicals

The N-H bond dissociation enthalpies (BDE's) of 40 anilines (pGC(6)H(4)NHY) from series 1 to 4 with alpha-Y and p-G substituents and the stability of related radicals (pGC(6)H(4)Ndot;Y) were studied using ab initio (MP2) and density functional methods (B3LYP) with large basis sets. The results show that both methods reproduce earlier experimental BDEs within 2-3 kcal/mol and satisfactorily predict the alpha and remote substituent effects on BDEs (DeltaBDEs), as they reproduced the experimental DeltaBDEs within less than 1 kcal/mol. Furthermore, the conventional radical stabilization enthalpy (RSE = - DeltaBDE) was found to be invalid to represent the trend of the radical stabilization because the molecule effect (ME) can contribute more to RSE than the radical effect (RE) for certain series (1 and 4). These radicals are in fact stabilized by electron-withdrawing groups (EWGs) but destabilized by electron-donating groups (EDGs), a phenomenon just opposite to the observed O-behavior of many other aromatic heteroatomic radicals studied so far. These radicals are thus assigned as a new radical class, Class counter-O (or O) according to Walter's terminology. Moreover, the excellent multi-parametric Hammett-type correlations indicated that the para substituent effects on BDEs originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. The atomic charge and spin population variations at a radical center due to p-G substitution were also found to correlate satisfactorily with REs. These results show that the spin delocalization effect should be explicitly considered in accounting for both DeltaBDEs and radical stabilization effects. Finally, an overall subsituent effect scale for radical stability has been proposed, and the overall substituent effect on the N-radicals was found to conform to the Capto-dative Principle.     

A novel reaction of the ‘Huisgen zwitterion’ with benzofuran-2,3-diones: an efficient strategy for the synthesis of spirocyclic benzofuran-2-one derivatives

The nitrogen-based nucleophile generated from azodicarboxylate and triphenylphosphine displayed good reactivity toward benzofuran-2,3-diones to generate a variety of spirocyclic benzofuran-2-one derivatives. The reactions accommodate a number of benzofuran-2,3-diones and different dialkylazodicarboxylates to give the enriched functionalized 3-spirooxadiazole benzofuran-2-ones with moderate to good yields (up to 93%).     

过渡金属-配体σ键键能在碳-氢键活化中的应用

过渡金属催化的碳-氢(C-H)键活化因其优异的原子经济性及步骤简便性在过去几十年间蓬勃发展,已成为当前构建复杂化合物最常用的策略之一.对该过程中活性中间体的热力学研究有助于加深人们对反应机理的理解,指导新催化剂、新反应的理性设计.然而,近年来该领域的发展颇为缓慢,相应的报道十分零散,缺少系统的归纳和总结.本综述简要梳理了过渡金属-配体σ键键能的研究历程,并举例阐述了这些热力学参数在分析反应可行性、判断反应选择性等方面的应用,旨在推动过渡金属络合物相关的热力学研究的快速发展.     

Remarkable rate acceleration of imidazole-promoted Baylis-Hillman reaction involving cyclic enones in basic water solution

The Baylis-Hillman reaction of cyclic enones was greatly accelerated in basic water solution with imidazoles as catalysts, which resulted in short reaction time, high yields, and expanding substrate scopes. Bicarbonate solution was shown to be the optimal reaction medium for the reaction in this study. The apparent "enhanced basicity" of imidazoles accounted for the rate increase in alkaline solution.     

Magnetic nanoparticle supported polyoxometalates (POMs) via non-covalent interaction: reusable acid catalysts and catalyst supports for chiral amines

Magnetic polyoxometalates (POMs) are obtained by a simple sonication between functionalized magnetic nanoparticles and polyoxometalates. This material can be used not only as a highly active acid catalyst, but also as a catalyst support for chiral amines.