Palladium-mediated intramolecular O-arylation: a simple route for the synthesis of quino[2,3-c] and quino[3,2-b]carbazoles

A simple route for the synthesis of quinocarbazoles in good yields via palladium-mediated intramolecular arylation involving ortho C-H activation is reported.     

Density functional theory rationalization of the substituent effects in trifluoromethyl-pyridinol derivatives

The influence of α-substitution in the structure, bonding and thermochemical properties of trifluoromethyl-pyridinol derivatives and their protonated counterparts has been studied by means of density functional theory. The geometries of the neutral and protonated species were optimized at the B3-LYP/6-311G(d,p) level of theory. Final energies were obtained through single point B3-LYP/6-311+G(3df,2p) calculations.The relative orientation of the different substituents within the heterocycle ring favours the formation of unexpected intramolecular hydrogen bonds (IHB), which have been characterized by means of the Atoms in Molecules theory of Bader. Although weak, these IHB are of great importance for understanding the gas phase structure and the thermodynamical properties of these compounds. Surprisingly, most of the substituted investigated pyridinols present proton affinities below or close to that calculated for the unsubstituted pyridine molecule. Only pyridinols bearing strong σ or π donor activating groups show proton affinities greater than that of pyridine.     

Stereoselective synthesis of hexahydroindoles and octahydrocyclohepta[b]pyrroles via gold(I)-catalyzed intramolecular 1,4-hydroamination of cyclic 1,3-dienes

The gold(I)-catalyzed intramolecular hydroamination of cyclohexa-1,3-dienes bearing an arylsulfonamide at the C-5 position proceeds in a 1,4-addition manner to afford hexahydroindole derivatives in a diastereoselective fashion and in good yields, whereas octahydrocyclohepta[b]pyrrole derivatives can be obtained from seven-membered ring substrates under the same reaction conditions. Coordination of the gold(I) species to the 1,3-diene at the double bond adjacent to the arylsulfonamide tether gave an η²-alkene gold complex. The anti-attack of the sulfonamide to the η²-alkene gold complex at the terminal position of the 1,3-diene resulted in the formation of the fused bicyclic ring with a newly formed Au-C bond at the allylic position. Allylic rearrangement of the η¹-allylgold complex followed by protodemetalation provided the fused heterobicyclic skeletons and regenerated the catalyst.     

Construction of novel spiroisoxazolines via intramolecular cyclization/methylation

Improved yields for the syntheses of a variety of spiroisoxazolines were achieved through intramolecular cyclization/methylation reactions of functionalized 5,5-disubstituted isoxazolines in one reaction vessel. Aromatic ring containing nitrile oxides and disubstituted geminal alkenes reacted in a 1,3-dipolar fashion to afford the corresponding 5,5-isoxazoline. A comparison of the relative location of the nucleophile and electrophile on the isoxazoline and two different ester functional groups was performed in order to determine the best isoxazoline system for the intramolecular cyclization/methylation reaction.     

Experimental and Theoretical Conformational Analysis of 5‐Benzylimidazolidin‐4‐one Derivatives – a ‘Playground’ for Studying Dispersion Interactions and a ‘Windshield‐Wiper’ Effect in Organocatalysis

The PF₆ salts of 5‐benzyl‐1‐isopropylidene‐ and 5‐benzyl‐1‐cinnamylidene‐3‐methylimidazolidin‐4‐ones 1 (Scheme) with various substituents in the 2‐position have been prepared, and single crystals suitable for X‐ray structure determination have been obtained of 14 such compounds, i.e., 2 – 10 and 12 – 16 (Figs. 2–5). In nine of the structures, the Ph ring of the benzyl group resides above the heterocycle, in contact with the cis‐substituent at C(2) (staggered conformation A ; Figs. 1–3); in three structures, the Ph ring lies above the iminium π‐plane (staggered conformation B ; Figs. 1 and 4); in two structures, the benzylic C? C bond has an eclipsing conformation ( C ; Figs. 1 and 5) which places the Ph ring simultaneously at a maximum distance with its neighbors, the CO group, the N?C‐π‐system, and the cis‐substituent at C(2) of the heterocycle. It is suggested by a qualitative conformational analysis (Fig. 6) that the three staggered conformations of the benzylic C? C bond are all subject to unfavorable steric interactions, so that the eclipsing conformation may be a kind of ‘escape’. State‐of‐the‐art quantum‐chemical methods, with large AO basic sets (near the limit) for the single‐point calculations, were used to compute the structures of seven of the 14 iminium ions, i.e., 3, 4 / 12, 5 – 7, 13 , and 16 (Table) in the two staggered conformations, A and B , with the benzylic Ph group above the ring and above the iminium π‐system, respectively. In all cases, the more stable computed conformer (‘isolated‐molecule’ structure) corresponds to the one present in the crystal (overlay in Fig. 7). The energy differences are small (≤2 kcal/mol) which, together with the result of a potential‐curve calculation for the rotation around the benzylic C? C bond of one of the structures, 16 (Fig. 8), suggests that the benzyl group is more or less freely rotating at ambident temperatures. The importance of intramolecular London dispersion (benzene ring in ‘contact’ with the cis‐substituent in conformation A ) for DFT and other quantum‐chemical computations is demonstrated; the benzyl‐imidazolidinones 1 appear to be ideal systems for detecting dispersion contributions between a benzene ring and alkyl or aryl CH groups. Enylidene ions of the type studied herein are the reactive intermediates of enantioselective organocatalytic conjugate additions, Diels–Alder reactions, and many other transformations involving α,β‐unsaturated carbonyl compounds. Our experimental and theoretical results are discussed in view of the performance of 5‐benzyl‐imidazolidinones as enantioselective catalysts.     

Photophysical Properties of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine

Spectral and photophysical investigations of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine (APT) have been performed in various solvents with different polarity and hydrogen-bonding ability.The emission spectra of APT are found to exhibit dual fluorescence in polar solvents, which attributes to the local excited and intramolecular charge transfer states, respectively. The two-state model is proven out for APT in polar solvent by the time-correlated single photon counting emission decay measurement. Interestingly, the linear relationships of different emission maxima and solvent polarity parameter are found for APT in protic and aprotic solvents, because of the hydrogen bond formation between APT and alcohols at the amino nitrogen N25. Furthermore, the effects of the complexation of the metal ion with tpy group of APT and the hydrogen bond formation between APT with methanol at the terpyridinenitrogen N4—N8—N14 are also presented. The appearance of new long-wave absorption and fluorescence bands indicates that a new ground state of the complexes is formed.     

Synthesis,Characterization and Crystal Structure of Some Novel 1‐Aryl‐2‐Thioxo‐2,3‐Dihydro‐1H‐Quinazolin‐4‐Ones

The base catalyzed intramolecular nucleophilic cyclization of 1‐(2‐haloaroyl)‐3‐aryl thioureas ( 1a‐i ), in the presence of DMF afforded the 1‐aryl‐2‐thioxo‐2,3‐dihydro‐1H‐quinazolin‐4‐ones ( 2a‐i ). The structures were confirmed by spectroscopic data, elemental analyses and in case of the 2c by single crystal X‐ray diffraction data. The mechanistic studies support an intramolecular nucleophilic substitution (S_NAr mechanism) rather than intramolecular aromatic substitution (S_RN1 mechanism).     

4,4′-[1,n-亚烷基双[(E)-2-(4-氧苯基)乙烯基]]双吡啶的光化学性质

通过E-[4-[2-(4-羟基苯基)乙烯基]吡啶与1,n-二溴烷烃亲核取代反应合成了4,4′-[1,n-亚烷基双[(E)-2-(4-氧苯基)乙烯基]]双吡啶[n=2(Ia),3(Ib),4(Ic),6(Id)].用元素分析、红外、紫外和质子核磁共振谱鉴定了Ia～Id的结构.将Ia～Id的稀溶液用中压汞灯和低压汞灯交替照射,发现其分子内光环加成反应的存在,并且随着亚烷基碳链的延长,反应速度加快.研究还发现锌离子可以与吡啶环上氮原子发生螯合作用使分子内光环加成反应加快.本文化合物荧光很弱,在较高浓度下有较强分子间激基缔合物荧光.     

链状双杂芳基乙烯化合物的合成与光化学性质研究

合成了1,n-双[4-[2-[2-(5-甲基苯并唑基)]乙烯基]苯氧基]烷烃(a:n=3;b:n=4;c:n=6)和2,2'-双[4-[2-[2-(5-甲基苯并唑基)]乙烯基]苯氧基]乙醚(d)4个新化合物.用元素分析、红外、紫外、核磁共振谱和质谱表征了其结构.用紫外吸收光谱跟踪研究了Ⅰa_Ⅰd在紫外灯照射下的变化,发现上述化合物在高压汞灯照射下可同时发生反顺异构化和[2+2]分子内光二聚两种反应,反顺异构化反应迅速可逆,而光二聚反应进行缓慢且不可逆.增加链长有助于提高分子内光二聚反应的速率.分子内光二聚反应不受空气中氧的影响的事实表明其是经激发单线态历程进行的.还发现分子内光二聚体在短波紫外光照射下容易进行逆[2+2]光解开环反应.上述化合物分子内光二聚和光解开环反应可以反复进行多次,表明该类化合物具有较高的光稳定性.     

N-(1-萘基)氨基乙酸的激发态分子内电荷转移和电子转移

氨基酸是蛋白质的基本结构单位 ,水溶液中基态氨基酸分子以内盐形式存在 [1] .由于质子化氨基的正诱导效应 ,羧基的离解常数显著提高 ,如氨基乙酸的羧基离解常数 ( 4.57× 1 0 -3mol/L,2 5℃ [1] )是乙酸 ( 1 .74× 1 0 -5 mol/L[2 ] )的 2 63倍 ;同时内盐结构亦使氨基酸和肽链具有分子内电偶极 ,后者已在肽链上电荷转移过程的调控中发挥重要作用 [3,4] .激发态氨基酸或肽的诱导效应和电偶极性质的研究尚未见报道 ,其主要原因可能是难有合适的激发方式和研究方法 .然而相关研究应予重视 ,因为研究结果将可能为生物酶活性的调节提供一种新的…