Solvent-free synthesis of naphthopyrans under ball-milling conditions

Under solvent-free ball-milling conditions, the nucleophilic addition reactions of terminal alkynes to carbonyl compounds promoted by KOH proceeded efficiently at ambient temperature. Subsequent cyclization reactions of the synthesized propargylic alcohols with 2-naphthol catalyzed by indium trichloride tetrahydrate, leading to the formation of naphthopyrans, were then investigated. In most cases, side reactions were avoided and thus high yields were achieved.     

Halogenation of ketones with N-halosuccinimides under solvent-free reaction conditions

Several aryl substituted ketones, cyclic ketones, 1,3-diketones and a β-ketoamide were halogenated with N-halosuccinimides under solvent-free reaction conditions (SFRC) at various temperatures (20-80 °C), whereas less enolized ketones required the presence of an acid catalyst (p-toluenesulfonic acid, PTSA). Bromination of substituted acetophenones obeys first order kinetics v=k_Br[ketone] and the following correlation with the keto-enol equilibrium constant: log k_Br=0.3pK_E+C₁, less enolized substrates being more reactive; the moderate positive charge developed in the rate determining step was confirmed by the Hammett correlation (ρ=−0.5). On the other hand, in cyclic ketones an opposite relation was observed: log k_Br=−0.6pK_E+C₂, indicating higher reactivity of substrates with higher enolization constant (K_E). The important role of the nature of the solvent (MeCN, MeOH) in preorganization of the ketone-NBS-PTSA mixture prior to SFRC bromination was found.     

Synthesis of vinyl sulfides via hydrothiolation of alkynes using Al2O3/KF under solvent-free conditions

We present here a clean, solvent-free hydrothiolation of alkynes using solid supported catalyst (Al₂O₃/KF). This efficient and improved method selectively furnishes the corresponding anti-Markovnikov vinyl sulfides in good to excellent yields. The method is applicable for aliphatic and aromatic thiols and the catalytic system can be re-used up to two times without previous treatment and with comparable activity.     

CH3COOH.TiO2: An excellent catalyst for the green nitration of toluene by N2O4

The solvent-free nitration of toluene with N₂O₄ gas over solid acid catalysts is a green reaction for preparing the mono-nitrotoluene (NT) isomers. The acid-modified catalysts are more efficient than common catalysts for this type of reaction. For this purpose, a titanium dioxide (TiO₂) catalyst is synthesized with a sol-gel method and modified by acetic acid to increase catalytic properties. The acid-modified TiO₂ (CH₃COOH·TiO₂) is characterized by different analyses. To optimization of toluene nitration conditions, reaction temperature (X₁) (30 < X₁ < 60 °C), N₂O₄/toluene molar ratio (X₂) (0.5 < X₂ < 2), and the amount of catalyst (X₃) (0.05 < X₃ < 0.3 g) factors were investigated by Minitab software with the CCD-RSM. Three responses including the selectivity of meta-NT isomer (S_m), the ratio of para-NT to ortho-NT selectivity (S_p/o), and the selectivity of by-products (S_bp) were considered for the optimization. Statistical parameters were applied to evaluate the goodness of fitting for the models. Optimum values for X₁, X₂, and X₃ parameters are 57.9 °C, 1.91, and 0.25 g, respectively. The conversion of toluene under these conditions is 93.2%. The comparison of S_m, S_p/o, and S_bp in CH₃COOH.TiO₂ (1.51%, 0.8, and 5.48%, respectively) with Fe₂O₃ (8.5%, 0.43, and 20.57%, respectively), SiO₂ (8.43%, 0.48, and 16.24%, respectively), TiO₂ (5.9%, 0.57, and 13.87%, respectively), TiO₂–Fe₂O₃ (4.72%, 0.64, and 9.18%, respectively), and TiO₂–SiO₂ (4.42%, 0.67, and 5.73%, respectively) catalysts show that this catalyst has a low S_m and S_bp as well as a higher S_p/o than other mentioned catalysts. The mechanism of the mentioned reaction is reviewed in the presence of CH₃COOH·TiO₂ catalyst. The high stability of the CH₃COOH·TiO₂ is proved by the reusability test, and it is found that its stability against inactivation is more than the TiO₂ catalyst.     

Microwave-assisted synthesis of new N4-[bi-（4-fluorophenyl）- methyl]-piperazine thiosemicarbazones under solvent-free conditions

Six new N4-[bi-（4-fluorophenyl）-methyl]-piperazine thiosemicarbazones 3a-f have been prepared starting from [bi-（4-fluorophenyl）-methyl]-piperazine in solvent-free condition under microwave irradiation with excellent yields. Their structures have been determined by elemental analysis, IR, MS and 1H NMR data.     

Cu(II)/polyimide linked COF: An effective mesoporous catalyst for solvent-free 1,5-benzodiazepine synthesis

Copper(II)@polyimide linked covalent organic frameworks (Cu@PI-COF) under solvent-free and microwave assisted conditions have been used in an efficient one-pot protocol for the preparation of 1,5-benzodiazepines via 1,2-diaminobenzene, aromatic aldehydes and dimedone. By applying solvent-free conditions and microwave irradiation, three-component condensation provides safe operations, low pollution, quick access to products, and an easy set-up. As a result of its reusability, the catalyst can also be reutilized many runs without missing any activity.     

无溶剂研磨法合成3-取代色满-4-酮衍生物及其抑菌活性研究

以6-卤代或未取代色满-4-酮为原料,在碱催化的条件下采用无溶剂研磨法与醛发生缩合反应,合成一系列新型的3-取代色满-4-酮衍生物3a~3t,并通过IR、1H NMR、13C NMR、HRMS对所合成的化合物进行结构表征。抑菌活性测试结果表明,所合成的化合物对大肠杆菌、枯草杆菌、金黄色葡萄球菌均有不同程度的抑菌活性。     

Regioselective synthesis of novel polyfunctionally substituted pyrazolo[1,5-a]pyrimidines under solvent-free conditions

A series of 2-(pyrazolo[1,5-a]pyrimidin-5-yl)benzoic acids 5 has been prepared by a novel protocol that uses the fusion method between 5-amino-1H-pyrazoles 4 and 3-(3-oxo-2-benzofuran-1(3H)-ylidene)pentane-2,4-dione 3. The use of this novel protocol renders good to excellent yields along with short reaction times. In addition, this solvent-free cyclocondensation proceeds in a regiospecific fashion by intramolecular ring opening of the furane ring in a Michael-type reaction.     

Native silica nanoparticle catalyzed anti-Markovnikov addition of thiols to inactivated alkenes and alkynes: a new route to linear and vinyl thioethers

A new route for the synthesis of linear and vinyl thioethers has been demonstrated using bare silica nanoparticle as catalyst at room temperature under solvent-free conditions. The catalyst can be reused up to six times without loss of catalytic activity.     

Silica-bonded S-sulfonic acid as a recyclable catalyst for chemoselective synthesis of 1,1-diacetates

A simple and efficient procedure for the preparation of silica-bonded S-sulfonic acid (SBSSA) by reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform is described. This solid acid is employed as a recyclable catalyst for the synthesis of 1,1-diacetates from aromatic aldehydes and acetic anhydride under mild and solvent-free conditions at room temperature.