A Facile One‐Pot Synthesis of Pyrrolo[1, 2‐a] Indoles by Intramolecular 1,3‐Dipolar Cycloaddition under Neat‐Microwave Irradiation

A straightforward and general approach for the stereoselective synthesis of fused pyrrolo[1,2‐a] indoles frameworks from>intramolecular 1,3‐dipolar cycloaddition using N‐alkylated Baylis–Hillman derivatives is presented. It was found that the cycloaddition proceeded efficiently under microwave irradiation in solvent‐free condition to afford highly stereoselective cycloadducts in good yield.     

On the “Tertiary Structure” of Poly‐Carbenes; Self‐Assembly of sp3‐Carbon‐Based Polymers into Liquid‐Crystalline Aggregates

The self‐assembly of poly(ethylidene acetate) (st‐PEA) into van der Waals‐stabilized liquid‐crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp³‐carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st‐PEA could perhaps be expected to lead directly to rigid‐rod behavior, molecular modeling reveals that individual st‐PEA chains are actually highly flexible and should not reveal rigid‐rod induced LC behavior. Nonetheless, st‐PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self‐aggregation of st‐PEA into higher‐order aggregates. According to MM/MD modeling st‐PEA single helices adopt a flexible helical structure with a preferred trans‐gauche syn‐syn‐anti‐anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self‐assemble into triple‐helical aggregates. Higher‐order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st‐PEA into higher‐order structures, and suggest the formation of rod‐like particles. The dimensions derived from these light‐scattering experiments correspond with st‐PEA triple‐helix formation. Langmuir–Blodgett surface pressure–area isotherms also point to the formation of rod‐like st‐PEA aggregates with similar dimensions as st‐PEA triple helixes. Upon increasing the st‐PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st‐PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface–solution interface with shapes and dimensions matching st‐PEA triple helices, in good agreement with the structures proposed by molecular modeling. X‐ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st‐PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st‐PEA. Formation of higher‐order aggregates explains the observed LC behavior of st‐PEA, emphasizing the importance of the “tertiary structure” of synthetic polymers on their material properties.     

Frequency dependence of phase-synchronization time in nonlinear dynamical systems

It has been found recently that the averaged phase-synchronization time between the input and the output signals of a nonlinear dynamical system can exhibit an extremely high sensitivity to variations in the noise level. In real-world signal-processing applications, sensitivity to frequency variations may be of considerable interest. Here we investigate the dependence of the averaged phase-synchronization time on frequency of the input signal. Our finding is that, for typical nonlinear oscillator systems, there can be a frequency regime where the time exhibits significant sensitivity to frequency variations. We obtain an analytic formula to quantify the frequency dependence, provide numerical support, and present experimental evidence from a simple nonlinear circuit system.     

Generation of 250 mW narrowband pulsed ultraviolet light by frequency quadrupling of an amplified erbium-doped fiber laser

We demonstrate a high-power, narrowband pulsed source at 390 nm by two stages of frequency doubling in periodically poled MgO:LiNbO(3) and periodically poled KTiOPO(4) of an amplified, passively mode-locked fiber laser. With a frequency quadrupling efficiency of 5.5% and a 0.1 nm bandwidth, the 250 mW ultraviolet source is a suitable compact pump source for many entanglement-based quantum information processing tasks.     

聚(4-乙烯基吡啶)硫酸氢盐: 一个新的高效催化剂用于无溶剂条件下合成13-芳香基-茚并 [1,2-b] 石脑油 [1,2-e] 吡喃-12(13H)-酮（英文）

An facile and efficient protocol for the synthesis of 13‐aryl‐indeno[1,2‐b]naphtha[1,2‐e]pyran‐ 12(13H)‐ ones has been developed that proceeds via the one‐pot three‐component sequential reaction of an aromatic aldehyde with β‐naphthol and 2H‐indene‐1,3‐dione under solvent‐free conditions in the presence of a poly(4‐vinylpyridinium)hydrogen sulfate(P(4‐VPH)HSO4) catalyst. The catalyst can be reused several times, making this procedure facile, practical, and sustainable. The simple experimental procedure, solvent‐free reaction conditions, use of an inexpensive catalyst, short react time, and excellent yields are some of the major advantages of this methodology.     

An eco-friendly catalytic route for one-pot synthesis of 2-amino-6-(2-oxo-2Hchromen-3-yl)-4-arylnicotinonitrile derivatives by silica-supported perchloric acid (HClO4–SiO2) under solvent-free conditions

A facile and environmentally benign synthesis of some 2-amino-6-(2-oxo-2H-chromen-3-yl)-4-arylnicotinonitrile derivatives from the reaction of 3-acetylcoumarin, aromatic aldehydes, and malononitrile under solvent-free condition in the presence of silica-supported perchloric acid (HClO₄–SiO₂) is described. The ability to reuse the catalyst, the high yields, and ease of purification are the important features of this process.     

Aqueous media preparation of 2-amino-4,6-diphenylnicotinonitriles using cellulose sulfuric acid as an efficient catalyst

A convenient approach to the synthesis of 2-amino-4,6-diphenylnicotinonitriles via four-component reaction of aromatic aldehydes, acetophenone derivatives, malononitrile and ammonium acetate is described. The reactions were done in water as solvent using cellulose sulfuric acid as catalyst. This simple protocol offer advantages such as shorter reaction times, simple work-up procedure, excellent yields and catalyst recovery.