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.     

A photoionization study of the charge transfer reactions: Xe+ + O2 → O+2 + Xe and O+2 + Xe → Xe+ + O2

Photoionization mass spectrometer techniques have been employed to study the charge transfer reactions: Xe⁺ + O₂ → O⁺₂ + Xe and O⁺₂ + Xe → Xe⁺ + O₂. The results show the reaction of Xe⁺(²P_{$\text{3}\text{2}$}) ions with O₂ molecules is much more efficient than the reaction of Xe⁺(²P_{$\text{1}\text{2}$}) ions with O₂ molecules. The charge transfer reaction of O⁺₂ ions with Xe atoms was detected for O⁺₂ ions in the a ⁴Π_u state.     

Tethered 2 + 2 + 2 cycloaddition reactions of cobalt-cycloheptyne complexes

Cycloheptyne-dicobalt hexacarbonyl complexes, substituted by propargylic ether functions, undergo 2 + 2 + 2 cycloaddition reactions with alkynes to give tricyclic benzocycloheptanes; an all-intramolecular version of this transformation is also possible.     

NHC-catalyzed enantioselective [2 + 2] and [2 + 2 + 2] cycloadditions of ketenes with isothiocyanates

The enantioselective N-heterocyclic carbene-catalyzed formal [2 + 2] and [2 + 2 + 2] cycloaddition of ketenes and isothiocyanates were developed. Reaction with N-aryl isothiocyanates at room temperature favors the [2 + 2] cycloaddition, while reaction with N-benzoyl isothiocyanates at -40 °C favors the [2 + 2 + 2] cycloaddition.     

Intracellular Ruthenium-Promoted (2+2+2) Cycloadditions

Metal-mediated intracellular reactions are becoming invaluable tools in chemical and cell biology, and hold promise for strongly impacting the field of biomedicine. Most of the reactions reported so far involve either uncaging or redox processes. Demonstrated here for the first time is the viability of performing multicomponent alkyne cycloaromatizations inside live mammalian cells using ruthenium catalysts. Both fully intramolecular and intermolecular cycloadditions of diynes with alkynes are feasible, the latter providing an intracellular synthesis of appealing anthraquinones. The power of the approach is further demonstrated by generating anthraquinone AIEgens (AIE=aggregation induced emission) that otherwise do not go inside cells, and by modifying the intracellular distribution of the products by simply varying the type of ruthenium complex.     

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.     

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 of acetylenes

Wilkinson's catalyst RhCl(PPh₃)₃ is an effective catalyst (0.5 – 2 mole %) for the rapid intermolecular trimerisation of 1,6-heptadiynes with monoacetylenes under mild conditions.     

Alkenes in [2+2+2] Cycloadditions

Participation of alkenes and allenes in [2+2+2] cycloaddition reactions has attracted much attention recently. This version of the well‐established alkyne cyclotrimerization renders interesting products, such as cyclohexadienes and other polycycles, through cascade processes. Many mechanistic variations are observed when using certain metal complexes as catalysts. The frequent generation of stereogenic centers has prompted the development of efficient asymmetric versions. This Minireview summarizes the efforts reported to date on the use of double bonds as partners in [2+2+2] cyclotrimerizations.     

Kinetics of the reactions Br + NO2 + M and I + NO2+ M

The reactions Br + NO₂ + M → BrNO₂ + M (1) and I + NO₂ + M → INO₂ + M (2) have been studied at low pressure (0.6-2.2 torr) at room temperature and with helium as the third body by the discharge-flow technique with EPR and mass spectrometric analysis of the species. The following third order rate constants were found k₁₍₀₎ = (3.7 ± 0.7) × 10^?31 and k₂₍₀₎ = (0.95 ± 0.35) × 10^?31 (units are cm⁶ molecule^?2 s^?1). The secondary reactions X + XNO₂ → X₂ + NO₂ (X = Br, I) have been studied by mass spectrometry and their rate constants have been estimated from product analysis and computer modeling.     

Formal [(2+2)+2] and [(2+2)+(2+2)] nonconjugated dienediyne cascade cycloadditions

[reaction: see text] Fluoranthene 2 and heptacycle 3 are easily accessible from the reaction of diyne 1 and norbornadiene (NBD) in the presence of the rhodium catalyst. The unusual [(2+2)+(2+2)] adduct 3 was confirmed by the X-ray crystal structure analysis.     

Novel [2 + 2 + 2 + 1] cycloaddition of enediynes catalyzed by rhodium complexes

[reaction: see text] The first Rh-catalyzed intramolecular [2 + 2 + 2 + 1] cycloaddition reaction of enediynes and CO is reported. This novel higher order cycloaddition process gives the corresponding 5-7-5 ring systems in high yield and selectivity. This process is another significant addition to the arsenal of cycloaddition-based synthetic methods, which provide powerful tools for rapid and efficient construction of complex polycyclic systems.     

Triptycenediols by rhodium-catalyzed [2+2+2] cycloaddition

An efficient, modular synthesis of triptycene derivatives is presented, in which the triptycene ring system is constructed from readily available anthraquinone and alkyne starting materials. A rhodium-catalyzed alkyne cyclotrimerization reaction serves as the key step in this new method for the preparation of these useful unnatural products.     

Ga2S3∶Eu2+和SrGa2+xS4+y∶Eu2+系列荧光粉的发光性能研究

采用高温固相法合成了Ga2S3∶Eu2+和SrGa2S4∶Eu2+系列荧光粉. 发现Ga2S3∶Eu2+的发射峰位于570 nm附近, SrGa2S4∶Eu2+的发射峰位于535 nm附近. 同时进一步探讨了SrGa2+xS4+y∶Eu2+体系中, 过量的Ga对发光的影响, 通过漫反射光谱和XRD谱确定过量的Ga是以Ga2S3的形式存在于SrGa2S4相中; 通过荧光光谱发现过量的Ga并不引起SrGa2S4∶Eu2+发射峰的位移, 而是增强其在400～520 nm处激发峰的强度, 从而增强Eu2+在535 nm处的发光强度.     

Synthesis of macrocycles via cobalt-mediated [2 + 2 + 2] cycloadditions

We investigated the formation of macrocycles from alpha,omega-diynes in cobalt-mediated co-cyclotrimerization reactions. Long-chain alpha,omega-diynes underwent metal-mediated [2 + 2 + 2] cycloadditions with nitriles, cyanamides, or isocyanates in the presence of CpCo(CO)2 (Cp = cyclopentadienide) to yield pyridine-containing macrocycles, i.e., meta- and para-pyridinophanes, such as 5m/5p, 35m/35p, and 41m/41p. The regioselectivity of these reactions was affected by the length and type of linker unit between the alkyne groups, as well as by certain stereoelectronic factors. An analogous alpha,omega-cyano-alkyne, 28, combined with an alkyne to yield two isomeric meta-pyridinophanes, such as 5m and 29m, and an ortho cycloadduct (benzannulation product), such as 29o. We developed a reaction protocol for these cobalt-based [2 + 2 + 2] cycloadditions that involves markedly improved conditions such that this process offers a convenient, flexible synthetic approach to macrocyclic pyridine-containing compounds. For example, diyne 6 reacted with p-tolunitrile in 1,4-dioxane to give 7p and 7m (7:1 ratio) in 87% yield at a moderate temperature of ca. 100 degrees C in 24 h without photoirradiation or syringe-pump addition. Isocyanates were also effective reactants, as exemplified by the formation of 44p almost exclusively (44p:44m > 50:1) in 64% yield from diyne 8 and 2-phenylethylisocyanate. By using this improved protocol we were able to co-cyclotrimerize long-chain alpha,omega-diynes with alkynes in certain cases to demonstrate a successful macrocyclic variant of the Vollhardt reaction. For instance, diyne 6 reacted with dipropylacetylene to give paracyclophane 57p and benzannulene 57o (2:1 ratio) in 29% yield.