Synthesis of six- and seven-membered heterocycles under ultrasound irradiation

This review gives an overview of utilization of ultrasound for the synthesis of various heterocyclic compounds. Ultrasonic irradiation has been considered as an efficient methodology in many organic syntheses. With ultrasonic assistance short reaction times, good selectivity and high yields are reported. The use of ultrasound irradiation in organic reactions has been increasing rapidly in recent years.     

Novel Access to Organostannane Compounds under Ultrasound Irradiation

A simple and efficient procedure has been developed for the synthesis of organostannane compounds by one-pot reaction of stannane halides, magnesium turnings and organic halides in the presence of 1,2-dibromoethane under ultrasound irradiation.     

A Novel Access to Organostannane Compounds under Ultrasound Irradiation

A simple and efficient procedure has been developed for the synthesis of organostanane compounds by one-pot reaction of stannane halides,magnesium turnings and organic halides in the presence of1,2-dibromoethane under ultrasound irradiation for the first time.     

An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-ones catalyzed by thiamine hydrochloride in water under ultrasound irradiation

An environmentally benign aqueous Biginelli protocol for the synthesis of substituted 3,4-dihydropyrimidin-2(1H)-ones using thiamine hydrochloride as a catalyst has been achieved. These ultrasound-assisted reactions proceed efficiently in water in the absence of organic solvent. Utilization of ultrasound irradiation, simple reaction conditions, isolation, and purification makes this manipulation very interesting from an economic and environmental perspective.     

Green method for ultrasensitive determination of Hg in natural waters by electrothermal-atomic absorption spectrometry following sono-induced cold vapor generation and ‘in-atomizer trapping’

Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO₂, H₂ and H₂O, the amount of lab wastes is minimized and a green methodology is achieved.     

Double Michael Addition Reaction of Bischalcone under Ultrasound

The Michael addition of 1,5-diaryl-1,4-pentadien-3-ones with active methylene compounds has been the subjects of many investigations. Ultrasound has increasingly been used in organic synthesis in the last three decades. Compared with traditional methods, this method is more convenient and easily controlled. A large number of organic reactions can be carried out in higher yield, shorter reaction time or milder conditions under ultrasonic irradiation. KF/Al2O3 as a useful solid supported catalyst has received considerable attention because of their high level of chemoselectivity and environmental compatibility as well as simplicity of operation and their ready availability at low cost. Herein we report the double Michael addition of dibenzalacetone with active methlene compounds such as dimethyl malonate, diethyl malonate,methyl cyanoacetate and ethyl cyanoacetate catalyzed by KF/Al2O3 under ultrasound irradiation.     

Molecular sieves: an efficient and reusable catalyst for multi-component synthesis of dihydropyrano[2,3-C]pyrazole derivatives

An efficient synthesis of dihydropyrano[2,3-C]pyrazole derivatives catalyzed by molecular sieves in ethanol under reflux and ultrasound irradiation has been described. The efficiency of catalyst has been compared with other aluminates and silicate based catalyst in order to optimize catalyst for the said organic transformation. This protocol is very useful due to easy recovery of the catalyst and its reusability, short reaction time, excellent yields, and avoidance of environmentally hazardous solvents.     

Altering Phase Separation in Aqueous Nonionic Surfactant Solutions by Power Ultrasound

Cloud point extraction (CPE) is an efficient and green separation technology as an alternative to conventional organic solvent extractions. How to accelerate the phase separation of aqueous surfactant solutions conveniently is of great importance. In this study, the effect of power ultrasound on the phase separation of aqueous solutions of a nonionic surfactant, Triton X-114 [(1,1,3,3-tetramethylbutyl) phenyl-polyethylene glycol], has been studied as a function of temperature by means of rheo-small angle light scattering. It is found that anomalous viscosity enhancements and micron-sized scattering aggregates are observed for the surfactant solutions after ultrasound irradiation. The aggregate growth is quantified by the characteristic length of the aggregates. It is proposed that ultrasonic cavitation can promote the aggregation or transition of surfactants in the aqueous solutions, resulting in the formation of micrometer-scale phase-separated droplets. This work may advance further understanding of the controlled transformation of aggregates in surfactant solutions via power ultrasound and promote its applications in CPE.     

Oxidation of Primary Aromatic Amines under Irradiation with Ultrasound and/or Microwaves

The oxidation of primary aromatic amines, p-methylaniline, p-ethylaniline and p-chloroaniline to the corresponding azo- and azoxy-compounds has been observed in ultrasound and/or microwaves systems. The individual irradiation of microwaves and its simultaneous irradiation with ultrasound obviously elevate the conversion of amines, as compared with the individual irradiation of ultrasound and the heating in a plain water bath. However, the formation of formamidine resulted in poor selectivity toward azo and azoxy products in the presence of dimethylformamide (DMF).     

片呐醇的绿色合成

综述了近年来片呐醇绿色合成研究的新进展,主要包括微波、超声波、固相合成、电合成、光化学合成等新技术、新试剂在该反应中的应用。     

片呐醇的绿色合成

综述了近年来片呐醇绿色合成研究的新进展，主要包括微波、超声波、固相合成、电合成、光化学合成等新技术、新试剂在该反应中的应用。     

The effects of ultrasound frequency and power on the activation energy in Si-KOH reaction system

The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz （interval by 20kHz） and 10-50W （interval by 10W）, respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate.     

Amberlyst-15–Catalyzed Synthesis of 2-Substituted 1,3-Benzazoles in Water under Ultrasound

A clean and general method has been developed for the synthesis of benzothiazole, benzoxazole, and benzimidazoles using Amberlyst-15 as a recyclable catalyst under ultrasound irradiation in water. The methodology is operationally simple, free from the use of hazardous organic solvents, and does not require the use of inert or anhydrous atmosphere. A number of 1,3-benzazole derivatives were prepared in good to excellent yields by using this methodology.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Ultrasound responsive organogels based on cholesterol-appended quinacridone derivatives with mechanochromic behaviors

A series of cholesterol-appended quinacridone (QA) derivatives 1a-1d have been synthesized,in which 1b and 1c could form stable organogels in a wide range of organic solvents upon ultrasound irradiation.Field emission scanning electronic microscope (FESEM) and transmission electron microscopy (TEM) of xerogels or precipitates indicated that 1b and 1c formed 1D fibrous nanostructure,while 1a assembled into 3D flower-like microstructures.The ultrasound-induced organogel process was characterized by kinetic UV...     

Efficient Synthesis of Five Types of Heterocyclic Compounds via Intramolecular Elimination Using Ultrasound‐Static Heating Technique

An experimental technique, ultrasound‐static heating, has been developed for the efficient synthesis of heterocyclic compounds. The technique involves ultrasonic irradiation and static heating processes. First, the ultrasonic irradiation process is performed to form an intermediate of the heterocyclic compound under mild conditions and the subsequent static heating process (heating the intermediate under solvent‐free conditions without stirring) produces the target heterocyclic compounds via intramolecular elimination.     

A green approach for synthesis of naphthoquinone-fused oxazine derivatives in water under ultrasonic irradiation

An efficient and eco-friendly procedure has been developed for synthesis of naphthoquinone-fused oxazine derivatives via one-pot pseudo four-component reaction of 2-hydroxy-1,4-naphthoquinone, aromatic amine and formaldehyde in water under ultrasound irradiation. This protocol has the advantages of being catalyst-free, with short reaction times and high yields, and being environmentally benign with an easy work-up.     

Ultrasound-Assisted Synthesis of 5<Emphasis Type="Italic">H</Emphasis>-Chromeno[2,3-<Emphasis Type="Italic">b</Emphasis>]pyridine Derivatives

An environmentally friendly method has been developed for the preparation of 5H-chromeno[2,3-b]pyridine derivatives in an aqueous medium under ultrasound irradiation.     

Synthesis of a Metal–Organic Framework Material,Iron Terephthalate,by Ultrasound,Microwave, and Conventional Electric Heating: A Kinetic Study

A metal–organic framework material named MIL‐53(Fe), iron terephthalate, has been synthesized sovothermally at a relatively low temperature by not only conventional electric (CE) heating, but also by irradiation under ultrasound (US) and microwave (MW) conditions to gain an understanding of the accelerated syntheses induced by US and MW. The kinetics for nucleation and crystal growth were analyzed by measuring the crystallinity of MIL‐53(Fe) under various conditions. The nucleation and crystal growth rates were estimated from crystallization curves of the change in crystallinity with reaction time. The activation energies and pre‐exponential factors were calculated from Arrhenius plots. It was confirmed that the rate of crystallization (both nucleation and crystal growth) decreases in the order US>MW?CE, and that the accelerated syntheses under US and MW conditions are due to increased pre‐exponential factors rather than decreased activation energies. It is suggested that physical effects such as hot spots are more important than chemical effects in the accelerated syntheses induced by US and MW irradiation. The syntheses were also conducted in two steps to understand quantitatively the acceleration induced by MW and it was found that the acceleration in crystal growth is more important than the acceleration in nucleation, even though both processes are accelerated by MW irradiation.     

Solvent-free Brønsted acid-catalyzed Michael addition of nitrogen- and carbon-containing nucleophiles by ultrasound activation

A new method has been developed for the Michael addition of nitrogen- and carbon-containing nucleophiles to cyclic enones. Using this conjugate addition reaction, a variety of different nucleophiles can react with a range of cyclic enones in the presence of p-toluenesulfonic acid under solvent-free ultrasound irradiation conditions affording the corresponding C–N or C–C adducts in good to excellent yields. Comparatively, performing the reaction under ultrasound irradiation gives higher yields, is more efficient and environmentally benign than performing it at high pressure.     

Application of Microwave Irradiation to Rapid Organic Inclusion Complex

Microwave irradiation has been used in chemical laboratories for moisture analysis and wet asking procedures of biological and geological materials for a number of years [1]. More recently the microwave irradiation also widely used for rapid organic synthesis [2]. However, there have not yet been any reports concerning the ultilisatioin of microwave ovens in the routine organic inclusion complex regularly in chemical research.