PtI2-catalyzed tandem 3,3-rearrangement/Nazarov reaction of arylpropargylic esters: synthesis of indanone derivatives

An efficient PtI(2)-catalyzed tandem reaction of arylpropargylic esters, involving 3,3-rearrangement and Nazarov reaction, has been developed to produce 3-substituted and 3,3-disubstituted indanone derivatives. This approach provided a pathway to the synthesis of indanone skeletons in natural products.     

PtCl2-Promoted cyclopropane opening in [4+2+2] homo Diels-Alder cycloadducts

A new and readily available catalytic system has been developed to open the cyclopropane ring in [4+2+2] homo Diels-Alder cycloadducts formed by reaction of norbornadienes and 1,3-butadiene. The cobalt-mediated homo Diels-Alder reaction followed by this PtCl₂-promoted isomerization is a key step in the efficient route to bicyclo[5.3.0]decanes, core of numerous natural products.     

Silicon-initiated carbonylative carbotricyclization and [2+2+2+1] cycloaddition of enediynes catalyzed by rhodium complexes

The reaction of dodec-11-ene-1,6-diynes or their heteroatom congeners with a hydrosilane catalyzed by Rh(acac)(CO)2 at ambient temperature and pressure of CO gives the corresponding fused 5-7-5 tricyclic products, 5-oxo-1,3a,4,5,7,9-hexahydro-3H-cyclopenta[e]azulenes or their heteroatom congeners, in excellent yields through a unique silicon-initiated cascade carbonylative carbotricyclization (CO-SiCaT) process. It has also been found that the 5-7-5 fused tricyclic products can be obtained from the same type of enediynes and CO through a novel intramolecular [2+2+2+1] cycloaddition process. The characteristics of these two tricyclization processes and the fundamental differences in their reaction mechanisms are discussed. This novel higher-order cycloaddition reaction has also been successfully applied to the tricyclization of undeca-5,10-diyn-1-als, affording the corresponding 5-7-5 fused-ring products bearing a seven-membered lactone moiety. Related [2+2+2] tricyclizations of enediyne and diynal substrates are also discussed. These newly discovered reactions can construct multiple bonds all at once, converting linear starting materials to polycyclic compounds in a single step. Thus, these new processes provide innovative routes to functionalized polycyclic compounds that are useful for the syntheses of natural and unnatural products.     

Rapid assembly of polycyclic substances by a multicomponent cascade (4 + 2)-(2 + 2) cycloadditions: total synthesis of the proposed structure of paesslerin A

A versatile method for stereoselective formation of multisubstituted bicyclo[4.2.0]octane framework has been developed by means of catalytic (4 + 2)-(2 + 2) cycloaddition reactions. Its application to the synthesis of a substance reported to be the cytotoxic sesquiterpene, paesslerin A, is described, and it has been made clear that a revision of the structure of natural paesslerin A is required.     

Heavy metal (Cd2+, Ni2+, Pb2+ and Ni2+) adsorption in aqueous solutions by oxidized starches

Superabsorbent materials based on natural products have been synthesized by free radical oxidation of corn starch using a redox system consisting of potassium permanganate and sodium bisulfite. The resulting oxidized starches were characterized by analyzing the variation of carbonyl and carboxyl contents. The swelling ability of these samples has been determined by gravimetric method in water and in saline solutions. The effect of oxidant concentration and bleaching procedure on the water absorption capacity has been studied. The ability to remove heavy metals in water solution has been tested against Cd²⁺, Ni²⁺, Pb²⁺ and Zn²⁺ ions, showing higher percentage of remotion for the unbleached oxidized starches, in particular against nickel ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Solid-supported [2+2+2] cyclotrimerizations

The transition-metal-catalyzed [2+2+2] cyclotrimerization of a diyne and an alkyne provides a convergent route to highly-substituted aromatic rings. This reaction possesses distinct drawbacks, especially low chemo- and regioselectivities, which hamper its application in combinatorial synthesis. These problems have been solved by the development of solid-supported [2+2+2]-cycloaddition reactions. If conducted on a solid-support, this reaction enables rapid combinatorial access to diverse sets of carbo- and heterocyclic small-molecule arrays. The scope of this methodology has been investigated by examining different immobilization strategies, different diyne precursors, and a variety of functionalized alkyne reaction partners. Overall, isoindoline, phthalan, and indan libraries were assembled in good to excellent yields and with high purities.     

Rapid Access to 2‐Methylene Tetrahydrofurans and γ‐Lactones: A Tandem Four‐Step Process

A one‐pot tandem process involving hydrolysis, Knoevenagel condensation, Michael addition, and Conia‐ene (HKMC) reactions has been developed for the rapid synthesis of indanone‐fused 2‐methylene tetrahydrofurans from the reaction of enynals and propynols. In this process, two rings and four bonds are generated with 100 % atom‐economy and high step‐efficiency. The resulting tetrahydrofurans were readily oxidized into α‐methylene γ‐lactones, which are one of the most important substructures in natural and bioactive compounds.     

UO 2 2+ sorption on bentonite

The capacity of bentonite and purified bentonite to remove UO ₂ ²⁺ ions from aqueous solutions has been investigated. The UO ₂ ²⁺ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO ₂ ²⁺ uptake was 1.010±0.070 meq UO ₂ ²⁺ /g of bentonite and 0.787±0.020 meq UO ₂ ²⁺ /g of purified bentonite. In purified bentonite UO ₂ ²⁺ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis.     

Pyridines via solid-supported [2 + 2 + 2] cyclotrimerization

The formation of pyridines via a crossed [2 + 2 + 2] cycloaddition has been achieved on a solid-support for the first time.     

Phenanthridine synthesis via [2+2+2] cyclotrimerization reactions

A concise synthesis of phenanthridines via a microwave-assisted [2+2+2] cyclotrimerization reaction has been developed.     

Rhodium‐Catalyzed [3+2+2] and [2+2+2] Cycloadditions of Two Alkynes with Cyclopropylideneacetamides

It has been established that a cationic rhodium(I)/H₈‐binap complex catalyzes the [3+2+2] cycloaddition of 1,6‐diynes with cyclopropylideneacetamides to produce cycloheptadiene derivatives through cleavage of cyclopropane rings. In contrast, a cationic rhodium(I)/(S)‐binap complex catalyzes the enantioselective [2+2+2] cycloaddition of terminal alkynes, acetylenedicarboxylates, and cyclopropylideneacetamides to produce spiro‐cyclohexadiene derivatives which retain the cyclopropane rings.     

Recent advances in [2+2+2] cycloaddition reactions

The [2+2+2] cycloaddition is an elegant, atom-efficient and group tolerant process for the synthesis of carbo- and heterocycles, mostly aromatic, involving the formation of several C-C bonds in a single step. Cyclotrimerisation is catalyzed by a variety of organometallic complexes, including more than 15 different metals. The aim of this tutorial review is to point out the most recent advances in this field and to encourage the use of this reaction enroute to complex molecules. After summarizing the most common catalysts and reaction conditions generally used, we survey the mechanistic features currently accepted for this reaction. Section 4 covers the scope of the different [2+2+2] cycloaddition versions starting with the cyclotrimerisation of three triple bonds, including nitriles, with especial emphasis on asymmetric reactions that create central, axial or planar chirality. Then, reactions that use double bonds are addressed. Finally, the most outstanding examples of natural products synthesis using [2+2+2] cycloadditions as a key step reported recently are shown.     

矿物发光原料方解石中含Fe2+猝灭杂质的去除

发光材料;猝灭物;矿物发光原料方解石中含Fe2+猝灭杂质的去除     

New calculations on the ion-molecule processes C2H2(+) + H2 --> C2H3(+) + H and C2H2(+) + H2 --> C2H4+

New high-level quantum chemical calculations have been undertaken to understand the rates and mechanisms of the reactive and associative channels for the reactants C2H2(+) + H2. The reactive channel, which produces C2H3(+) + H, has been shown to be slightly endothermic, confirming earlier calculations at a somewhat lower level and in agreement with some recent experimental work. The associative channel, leading to C2H4+, has been shown to proceed via a transition state with negative energy relative to the reactants, so that association is predicted to be efficient. This result is in conflict with an earlier theoretical study but in agreement with low-temperature experimental measurements.     

Studies on Synthetic Inorganic Ion Exchangers-III Quantitative Separations of Mg2+ -Pb2+, Zn2+ - Pb2+ Cu2+ - Pb2+, Al3+ - Pb2+, Zn2+ - Cd2+, and Mg2+ - Cd2+ on Lead Antimonate Columns

Abstract

A new inorganic ion exchanger, lead antimonate has been synthesized having an Pb:Sb ratio of 1:5 and cation exchange capacity of 1.46 mequiv./g. It is fairly stable in water and dilute solutions of acids, bases and salts. Ion distribution studies on twenty metal ions have been determined on this gel at pH 1,2,3 and 5. The following mixtures have been separated: Mg²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Cu²⁺ - Pb²⁺, Al³⁺ - Pb²⁺, Zn²⁺ - Cd²⁺ and Mg²⁺ - Cd²⁺. Mg²⁺ and Al³⁺ were removed with 0.4 M ammonium nitrate, Cu²⁺ and Zn²⁺ with 0.4 M ammonium nitrate + 0.1M nitric acid (1:1), Pb²⁺ with 0.5M nitric acid and Cd²⁺ with 0.25M nitric acid. A tentative structure of this material is proposed on the basis of chemical analysis, pH titrations, thermogravimetry and IR spectrophotometry.     

Rhodium catalysed [2+2+2] cycloadditions- an efficient regiospecific route to calomelanolactone

A short regiospecific synthesis of calomelanolactone has been devised in which the key step is a [2+2+2] cycloaddition.     

Spectral analysis of Mn2+, Co2+ and Ni2+: B2O3-ZnO-PbO glasses

This paper reports on the spectral properties of Mn2+, Co2+ and Ni2+ ions doped B2O3-ZnO-PbO glasses. XRD, FT-IR spectra and DSC profiles of these glasses have also been carried out, and the FT-IR profiles have shown the presence of both BO3 and BO4 units. It is interesting to notice that the FT-IR peak positions are slightly shifted towards higher energy with an increase in transition metal ion concentration change. From the measured DSC thermograms, glass transition (T(g)), crystallization (T(c)) and temperature of melting (T(m)) have been evaluated. From the UV absorption spectra of Mn2+, Co2+ and Ni2+ ions doped glasses, both direct and indirect optical band gaps have been calculated. The visible absorption spectra of Mn2+:glasses have shown a broad absorption band at 520 nm (6A1g(S) --> 4T1g(G)); with Co2+ ions one absorption band at 605 nm (4A2(4F) --> 4T1(4P)) and another at 1450 nm (4A2(4F) --> 4T1(4F)); and for Ni2+:glasses three absorption bands at 420 nm (3A2g(F) --> 3T1g(P)), 805 nm (3A2g(F) --> 1Eg(D)) and 880 nm (3A2g(F) --> 3T1g(F)) have been observed. For Mn2+:glasses, upon excitation with 262 nm, a green emission (539 nm) with a slight blue shift; and with 392 nm, a green emission (534 nm) with a slight red shift with Mn2+ ions concentration change (0.2-0.5 mol%) has been observed. This green emission has been assigned to (4T1(G) --> 6A1(S)) d-d transition of Mn2+ ions that are in tetrahedral co-ordination. For 0.5 mol% Co2+ ions doped glass, upon excitation with 580 nm, a red emission (625 nm) has been observed which originates from 2E(2G) --> 4A2(4F) transition of Co2+ ions in tetrahedral co-ordination. For Ni2+ ions doped glasses upon excitation with 420 nm, a green (577 nm) and red (670 nm) emissions are observed and are assigned to (1T2g(D) --> 3A2g(F)) and (1T2g(D) --> 3T2g(F)) d-d transitions of Ni2+ ions in octahedral co-ordination.     

Recent progress in cobalt-mediated [2 + 2 + 2] cycloaddition reactions

For many years, our research group has been interested in the new developments of cobalt-mediated cyclizations. In this article, our recent achievements in the field of inter- and intramolecular [2 + 2 + 2] cyclizations are compiled.     

Recent advances in radical-mediated [2+2+m] annulation of 1,n-enynes

1,n-Enynes are a versatile class of unsaturated hydrocarbons that found broad applications in the synthetic community of natural products, biologically active structures and functional materials. Typical methods for the transformations of 1,n-enynes include the radical-mediated [2+2+m] annulation reaction as they are particularly efficient accesses to functionalized polycyclic compounds. We herein highlighted recent process in the radical-mediated [2+2+m] annulation of 1,n-enynes, including [2+2+1] and[2+2+2] modes, for the construction of five-to six-membered-ring-fused polycyclic scaffolds. Meanwhile, the mechanisms for these transformations were described.     

Thermodynamics of Pb2+ and Ni2+ adsorption onto natural bentonite from aqueous solutions

Removal of Pb2+ and Ni2+ from aqueous solutions by sorption onto natural bentonite was investigated. Experiments were carried out as a function of particle size, the amount of bentonite, pH, concentration of metals, contact time, and temperature. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich, and Dubinin-Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 303 K by batch experiments. The thermodynamic parameters (DeltaH,DeltaS,DeltaG) for Pb2+ and Ni2+ sorption onto bentonite were also determined from the temperature dependence. The adsorptions were endothermic reactions. The results suggested that natural bentonite is suitable as a sorbent material for recovery and adsorption of metal ions from aqueous solutions.