A new and efficient synthetic approach to dichlorofluoflavines. Study of the stability of isomeric fluoflavines by HF and B3LYP procedures

The first method for the synthesis of 7,10-dichloro-5,12-dihydroquinoxalino[2,3-b]quinoxalines is reported. Treatment of 3,3,6,6-tetrachloro-1,2-cyclohexanedione with diaminomaleonitrile leads to 5,8-dichloro-2,3-dicyanoquinoxaline in near quantitative yields. This compound has been found to be an excellent synthetic equivalent of unavailable 2,3,5,8-tetrachloroquinoxaline. It reacts with o-phenylenediamines providing the corresponding dichlorofluoflavines in fair to high yields. These compounds have been identified by NMR spectroscopy and X-ray crystallography. Molecular structures, chemical hardness, ΔG₂₉₈^≠-values, and relative stabilities of all possible isomeric products have been calculated by HF and B3LYP density functional theory methods.     

Facile aromatization of 3,4-dihydropyrimidin-2(1H)-ones(DHPMs) by iodine

A facile aromatization of 3,4-dihydropyrimidin-2(1H)-ones using iodine in dimethyl sulfoxide under microwave irradiation was carried out which is more efficient and gives high yield in less time;presently it is the most important catalyst for dehydrogenation.     

Mechanistic studies of highly regioselective decarboxylative-prenyl migration reactions of prenyloxycarbonyl-diketo-dioxinones

Mechanistic studies of tandem regioselective decarboxylation, prenyl transfer, and aromatization reactions of prenyl dioxinone diketo-carboxylates to provide 3-prenyl-resorcylate derivatives are described. Studies of the effects of concentration and the base employed as well as the results of cross-over experiments were all found to be consistent with the reaction proceeding largely via an intermolecular reaction pathway.     

Three‐Component,One‐Pot Synthesis of Pyrido[2,3‐d]pyrimidine Derivatives Catalyzed by KF‐alumina

Abstract

A series of pyrido[2,3‐d]pyrimidine derivatives were synthesized by the three‐component reaction of arylaldehyde, cyanoacetate, and 4‐amino‐2,6‐dihydroxylpyrimidine in ethyl alcohol at 80°C catalyzed by KF‐Al₂O₃. It was interesting that further aromatization took place automatically. Compared with other synthetic methods, this new method has the advantage of easier workup, milder reaction conditions, and good yields.     

Novel Transformation of Methoxy Tetralones During Demethylation with Boron Trifluoride Etherate and Acetic Anhydride

Abstract

Tetralones 3 and 9 on treatment with a mixture of boron trifluoride etherate and acetic anhydride underwent molecular transformations yielding the fully aromatized products 6 and 10, respectively, Oxidation of dimethoxy tetralin 13 with chromic acid and acetic acid afforded 6‐methoxy‐α‐tetralone 12.     

KHSO4 Supported Onto Bentonite,A Versatile Reagent for Aromatization of Hantzsch 1,4‐Dihydropyridines

Aromatization of Hantzsch 1,4‐dihydropyridines was promoted by KHSO₄, a relatively green chemical, supported onto bentonite to yield the corresponding pyridine derivatives in excellent yields. The reaction was carried out under mild and convenient conditions.     

Oxidative aromatization of 3,5-disubstituted 2-isoxazolines by nitric oxide

3,5-Disubstituted 2-isoxazolines were oxidized to corresponding isoxazoles by nitric oxide in dichloromethane. The reaction more likely occurred via a one-electron transfer process.     

Investigation of the aromatization of C6+ hydrocarbons on chromia/lanthana-zirconia catalyst: Part I. Catalytic experiments

The aromatization pathway on a chromia/lanthana-zirconia catalyst has been investigated by the conversion of 13 linear and branched hydrocarbons. The product distribution is determined by the educt structure and points to a mechanism without side reactions like isomerization or cracking. The differences in aromatization reactivities could be explained by a mechanism via a stepwise dehydrogenation to a conjugated triene structure. First calculations show that methyl or methylene groups close to terminal double bonds can stabilize these trienes. Such substrates show higher aromatic yields than those without stabilizing groups.     

Photoinduced Aromatization of Unsymmetrically Substituted 1,4‐Dihydropyridines

Irradiation of unsymmetrically substituted 1,4‐dihydropyridines ( 1b ‐ 1j ) while bubbling oxygen or argon through the solution resulted in aromatization to the corresponding pyridine derivatives ( 3b ‐ 3j ). Compound 1a with 2‐nitrophenyl substituent in 4‐position undergoes elimination of water upon irradiation under both oxygen and argon atmospheres and formation of 3a with 2‐nitrosophenyl substituent. On the other hand, irradiation of the compounds 1e , 1k and 1l with 4‐hydroxy‐3‐methoxyphenyl, 5‐methyl‐2‐furyl and 2‐furyl substituent in this position, respectively, resulted in the expulsion of these substituents and formation of a pyridine derivative unsubstituted in position 4, namely compound 2 . Chloroform as a solvent causes the photo‐oxidation of these compounds by an electron transfer mechanism which is supported by the formation of dichloromethane according to GC analysis and presence of acid (HCl) in the solution after irradiation.     

锌在ZnZSM-5沸石中的形态及其催化作用

采用NH_3－TPD和吡啶吸附红外光谱法，研究了不同含Zn量ZnHZSM-5沸石中Zn的存在状态．结果表明，用浸渍方式将Zn引入到HZSM-5沸石后，在NH_3－TPD谱上产生两个新的NH_3脱附峰．峰位分别在原HZSM－5沸石的低温峰与高温峰之间和比高温峰较高温区处，其相应的吸附中心分别以L_1、L_2表示．L_1可能与ZnHZSM－5沸石上ZnO物种相对应; L_2与吡啶吸附红外光谱的L_(1616)吸收带有关，可能与ZnHZSM-5上的ZnOH~＋物种相对应．丙烷芳构化反应结果表明，芳烃收率随L_2的脱附NH_3量的增加有一最宜值，而活性的稳定性则随之降低。