Solid-phase synthesis of 2-substituted 4-amino-7-oxo-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidines

An efficient solid-phase synthesis of 2-substituted 4-aminopyrido[2,3-d]pyrimidines 15 is reported. The procedure started by solid supporting a p-hydroxybenzaldehyde 8 to the Wang resin by using the Mitsunobu protocol. The resulting aldehyde 17 was treated with a substituted acid methyl malonate 10 to afford the corresponding alpha, beta-unsaturated ester 18, which was converted to the Michael adduct 21 by reaction with malononitrile. Cyclization of 21 with an amidine system 13 yielded the solid supported pyridopyrimidine 22, which afforded the corresponding 2-substituted 4-aminopyrido[2,3-d]pyrimidine 15 upon treatment with TFA:DCM. Compounds 15 present three diversity centers R1, R2 and R3. Having validated the chemistry on solid support, a 32-membered combinatorial library was obtained using this protocol.     

Solid-phase synthesis of 2-substituted 4-amino-7-oxo-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidines: An example of cyclization-assisted cleavage

An efficient solid-phase synthesis of 2-substituted 4-aminopyrido[2,3-d]pyrimidines 12 by cyclization-assisted cleavage from resin is reported. The procedure starts by solid supporting an ,-unsaturated acid 8 to the Wang resin 13 by using DCC and 4-DMAP in THF. The resulting ,-unsaturated ester 14 is converted to the Michael adduct by treatment with malononitrile in NaOMe/THF. Such Michael addition constitutes the first example of a Michael reaction with malononitrile in solid-phase. Finally, the Michael adducts 15 are treated with an amidine system in MeOH to yield the corresponding pyridopyrimidines 12. Compounds 12 present three diversity centers R1, R2 and G. Having validated the chemistry on solid support, a 40-membered combinatorial library was obtained using this protocol.     

A novel synthesis of highly substituted imidazo[1,5-a]pyrazine derivatives by 3-CR/2-CR sequence

By combining a three-component reaction of 2, 3-diaminomaleonitrile, ketones and isocyanides with a subsequent reaction of 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives obtained from isocyanide-based three-component reaction with various alkyl and aryl isocyanates or isothiocyanates can be assembled a new class of highly substituted imidazo[1,5-a]pyrazine derivatives.     

Synthesis of 2-arylamino substituted 5,6-dihydropyrido[2,3-d]pyrimidine-7(8H)-ones from arylguanidines

A practical protocol was developed for the synthesis of 2-arylamino substituted 4-amino-5,6-dihydropyrido[2,3-d]pyrimidin-7(8H)-ones from ??,??-unsaturated esters, malononitrile, and an aryl substituted guanidine via the corresponding 3-aryl-3,4,5,6- tetrahydropyrido[2,3-d]pyrimidin-7(8H)-ones. Such compounds are formed upon treatment of 2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles with an aryl substituted guanidine in 1,4-dioxane and are converted to the desired 4-aminopyridopyrimidines with NaOMe/MeOH through a Dimroth rearrangement. The overall yields of this three-step protocol are, generally speaking, higher than the multicomponent reaction, previously developed by our group, between an ??,??-unsaturated ester, malononitrile, and an aryl substituted guanidine.     

Parallel and automated library synthesis of 2-long alkyl chain benzoazoles and azole[4,5-<Emphasis Type="BoldItalic">b</Emphasis>]pyridines under microwave irradiation

Summary A versatile route to 40-membered library of 2-long alkyl chain substituted benzoazoles (1 and 2) and azole[4,5-b]pyridines (3 and 4) via microwave-assisted combinatorial synthesis was developed. The reactions were carried out in both monomode and multimode microwave oven. With the latter, all reactions were performed in high-throughput experimental settings consisting of an 8×5 combinatorial library designed to synthesize 40 compounds. Each step, from the addition of reagents to the recovery of final products, was automated. The microwave-assisted N-long chain alkylation reactions of 2-alkyl-1H-benzimidazole (1) and 2-alkyl-1H-benzimidazole[4,5-b] pyridines (3) were also studied.     

A One-Pot Entry to a Novel 3-H-benzo[d]pyrazolo[1,5-b]isothiazole Ring System

Summary The phosphorus ylide obtained from the reaction between 2-aminobenzo[d]isothiazol-3-one and dimethyl acetylenedicarboxylate in the presence of triphenylphosphine undergoes a smooth intramolecular Wittig-type reaction to produce, in a one-pot reaction, 3-H-benzo[d]pyrazolo[1,5-b]isothiazole-2,3a-dicarboxylic acid dimethyl ester, a novel functionalized heterocyclic compound.     

Diammonium hydrogen phosphate as a versatile and efficient catalyst for the one-pot synthesis of pyrano[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidinone derivatives in aqueous media

Diammonium hydrogen phosphate, (NH(4))(2)HPO(4), was used as a catalyst for one-pot, three-component condensation reactions consisting of aromatic aldehydes, malononitrile and barbituric/thiobarbituric acid in aqueous ethanol at room temperature. This method has the advantages of a simple operation, mild reaction conditions, high yields, by using a less toxic and low cost chemical as a catalyst.     

A green one-pot three-component cascade reaction: the synthesis of 2-amino-5,8-dihydro-3H-pyrido[2,3-D]pyrimidin-4-ones in aqueous medium

A one-pot three-component cascade reaction for the green synthesis of a new class of 2-amino-5,8-dihydro-3H-pyrido[2,3-d]pyrimidin-4-ones was developed from the condensation of aromatic aldehydes with 2,6-diaminopyrimidin-4(3H)-one and acetophenone derivatives or various cyclic ketones in the presence of a catalytic amount of sodium carbonate in a mixture of water and ethanol at 60  \({^{\circ }}\hbox {C}\). This reaction led to the construction of two carbon–carbon bonds and one carbon–nitrogen bond in a single synthetic step.     

Efficient synthesis of 2,3-disubstituted-2,3-dihydroquinazolin-4(1H)-ones catalyzed by dodecylbenzenesulfonic acid in aqueous media under ultrasound irradiation

Synthesis of 2,3-disubstituted-2,3-dihydroquinazolin-4(1H)-one derivatives catalyzed by dodecylbenzenesulfonic acid was carried out in 80–92% yields at 40–42 °C within 1–2 h in aqueous media via one-pot three-component condensation of isatoic anhydride, aromatic aldehyde and amine under ultrasound irradiation. Convenient work-up procedures, mild reaction conditions, avoiding the use of organic solvents, and friendly to environment are the salient features of this protocol.     

A novel three-component reaction for the synthesis of 3-aryl-4H-benzo [1,4] oxazin-2-amine

A high yielding and fast method for the synthesis of 3-aryl-4H-benzo [1,4] oxazin-2-amine via one-pot, three component reaction of an aromatic aldehyde, isocyanide and o-aminophenol using p-toluene sulfonic acid as a catalyst is described.     

The thermoelastic properties of [N(CH3)4]2ZnBr4 and [N(CH3)4]2MnBr4

The ferrodistortive phase transition in the bis-tetramethylammonium tetrabromide crystals below room temperature is studied within the framework of the Landau theory. The specific heats of [N(CH₃)₄]₂MnBr₄ and [N(CH₃)₄]₂ZnBr₄ are correctly described down to 40°C below the transition temperature. The phenomenological parameters are determined from calorimetric results, elastic constants and thermal expansion data. Using these coefficients, the monoclinic angle in the ferrodistortive phases is obtained. The anharmonic quantities, such as the isothermal compressibility, calculated from the specific heat data, are in good agreement with the values derived from the elastic measurements.     

The synthesis, characterization and optical properties of novel 1,3,4-oxadiazole-containing imidazo[1,5-a]pyridine derivatives

A series of novel substituted 1,3,4-oxadiazole derivatives were synthesized by the reaction of 3-butyl-1-chloroimidazo[1,5-a]pyridine-7-carbohydrazide with propionyl chloride and substituted benzoic chloride in the presence of phosphorus oxychloride. The compounds were characterized using IR, ¹H NMR, ¹³C NMR and HRMS. Absorption and fluorescence spectra were measured in dichloromethane; an intense absorption maxima was noted at ca. 290 nm and emission maxima was noted at ca. 470 nm. The absorption spectra of the 1,3,4-oxadiazole derivatives reveal that a phenyl and an ethyl group attached to the 1,3,4-oxadiazole ring markedly influenced the maximum absorption. The structures based on density function theory (DFT) calculation show planar configurations for the compounds. The calculated molecular orbital correlates well with their absorption.     

Investigation of the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by certain substituted uracils

The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by a series of uracils has been studied in water and acetonitrile solvents using steady-state and time-resolved fluorescence techniques. The steady-state fluorescence quenching technique has been performed in three different pHs (i.e. 4, 8 and 12). The bimolecular quenching rate constant (k_q) increases with increase in pH of uracils. In acidic pH, a pure hydrogen atom abstraction is proposed as the quenching mechanism. This is supported by a pronounced solvent deuterium isotope effect. Electron transfer from the anionic form of uracil to the excited state of DBO is proposed as a mechanism for quenching in basic pH on the basis of highly exergonic thermodynamics obtained from the Rehm-Weller equation. The variation of k_q is explained on the basis of the electronic effect of substitution in uracils as well.     

Mixed alkali metal selenate proton conductors: Phase transitions and crystal structure of [Rb0.54(Nh4)0.46]3H(SeO4)2

Optical birefringence, calorimetric, thermal expansion, powder and single crystal X-ray diffraction investigations of mixed proton conductors [Rb_1-x(NH₄)_x]₃H(SeO₄)₂ were performed with the aim of studying the influence of partial substitution of cations on the superprotonic phase transition, on the atomic structure and on other characteristic features of this type of crystals.     

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH₃)₄ groups.     

一种新型钼磷酸盐杂多化合物(NH3CH2CH2NH3)7H2[NaMo12O30(PO4)2(HPO4)5(H2PO4)]·7H2O的合成和光谱研究

本文采用水热反应条件 ,合成得到一种新型的含五价钼原子的杂多化合物 :(NH3CH2 CH2 NH3) 7H2[NaMo1 2 O30 (PO4 ) 2 (HPO4 ) 5(H2 PO4 ) ]·7H2 O ,在晶体结构测定的基础上对其进行红外、拉曼和紫外 可见漫反射光谱研究。结果表明 :较长的Mo(Ⅴ )—O键键长和分子内大量的氢键造成化合物红外光谱特征的红移。     

2-(咪唑[1,2-a]吡啶-2-基)-2-氧代乙酸自由基及其高氯酸盐的晶体结构和磁性

报道2-(咪唑[1,2-a]吡啶-2-基)-2-氧代乙酸自由基及其高氯酸盐的晶体结构,探索了晶体堆积结构或超分子相互作用与磁性能的关系．在两个晶体结构中,超分子相互作用(氢键、原子间密接触、负离子-π电子或孤对-π)使2-(咪唑[1,2-a]吡啶-2-基)-2-氧代乙酸自由基主要以抗磁性的二聚体存在并导致了低的磁化率．该自由基晶体展示了准一维的柱状堆积链和弱的反铁磁性,而氢键和负离子-π作用则诱导高氯酸晶体呈一维双股链结构并显示了弱的铁磁性．     

Ultrasound-promoted catalyst-free one-pot four component synthesis of 2H-indazolo[2,1-b]phthalazine-triones in neutral ionic liquid 1-butyl-3-methylimidazolium bromide

A catalyst-free one-pot four component methodology for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones under ultrasonic irradiation at room temperature using 1-butyl-3-methylimidazolium bromide, [Bmim]Br, as a neutral reaction medium is described. A broad range of structurally diverse aldehydes (aromatic aldehydes bearing electron withdrawing and/or electron releasing groups as well as heteroaromatic aldehydes) were applied successfully, and corresponding products were obtained in good to excellent yields without any byproduct.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.