Syntheses of ladder-type oligonaphthalene derivatives and their photophysical and electrochemical properties

Ladder-type oligophenylene derivatives are important compounds for light-emitting devices. However, the closely related ladder-type oligonaphthalene derivatives have received little attention due to the lack of synthetic accessibility. We hereby report the syntheses of these novel conjugated systems by means of an intramolecular cationic cyclization protocol. Utilizing a one-pot-multiple-component reaction, the acyclic precursors to these ladder-type oligomers up to pentamer can be synthesized from small fragments in just two or three steps. Photophysical and electrochemical studies revealed that the electron delocalization in these compounds is considerably enhanced relative to that found in the regular unplanarized oligonaphthalene derivatives. However, such an effect is much weaker than that found in fully planar rylene derivatives.     

Structure and stability of X4Y4H4 (XY=CC,BN)

Ab initio calculations have been carried out to study the structures and relative stabilities of the planar eight‐membered ring B₄N₄H₄ and its isoelectronic species C₈H₄ at the HF/6‐31G*, MP2/6‐31G*, MP2/6‐311G**, and MP4SDQ/6‐31G* levels. The analyses of Milliken population, vibration frequencies, π‐molecular orbital components, and orbital energy levels were used to evaluate the relative stabilities of these two similar systems. The homodesmotic reactions were also taken to be a useful index of relative stability for X₄Y₄H₄ (XY=CC, BN) and gave the resonance energies with MP4SDQ/6‐31G* of C₈H₄ (?37.2 kcal/mol) < B₄N₄H₄ (?29.2 kcal/mol). Furthermore, we calculated the thermodynamic functions of these reactions to discuss the influence of temperature. It is concluded that B₄N₄H₄ may exist in theory and could be a little more stable than C₈H₄. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 293–298, 2001     

Facile Syntheses of ABC Ring Skeleton of Camptothecin and Related Alkaloids

Abstract

Facile synthetic approaches toward the preparation of ABC ring of camptothecin and related alkaloids starting from cheaper and readily available chemical reagents.     

Ca~(2+)增敏米诺环素荧光显微成像技术应用于米诺环素的检测

应用固载表面毛细流自组装环荧光显微成像技术,建立了Ca2+增敏米诺环素荧光体系测定牛奶中米诺环残留量的分析方法。将米诺环素溶液与一定量的氯化钙溶液,pH 8.50的氨性缓冲溶液及PVA-124溶液充分混合均匀。反应10 min后,滴在疏水性载玻片表面上,微波加热,溶剂受热挥发后,形成直径约为1.7 mm,环带宽约为45.3μm的自组装环。当点样体积为0.3μL时,线性范围为5.6×10-13~1.8×10-11mol,方法的检出限(3σ)为5.6×10-14mol。应用于米诺环素胶囊中米诺环素和牛奶中残留米诺环素的检测,回收率分别为104.3%~105.0%和96.0%~105.9%,相对标准偏差(n=5)小于3.5%。     

Lactide Polymerisation with Air‐Stable and Highly Active Zinc Complexes with Guanidine–Pyridine Hybrid Ligands

New class of air‐stable catalysts for lactide polymerisation: Guanidine–pyridine hybrid ligands (picture, left) were used to prepare a series of zinc complexes (e.g., depicted cation [ZnL₂(CF₃SO₃)]⁺, where L is the quinoline‐containing ligand with R¹=R²=R³=R⁴=Me), in which the ligand binds through two different N‐donor atoms. The zinc complexes show high activity in ring‐opening polymerisation of d,l ‐lactide (right), giving polylactide with molecular masses up to 176 000 g mol^?1 and in high yield.

     

Synthesis of dihydroxyoligophenylenes containing π-deficient or π-excess hetero-aromatic rings and their solvatochromic behavior

Dihydroxyoligophenylenes (HO-ArPh(m)-OHs) with 9,9-dihexyl-2,7-fluorene (Ar=Flu), 2,5-dioctyloxy-1,4-benzene (Ar=Dob), pyridine (Ar=Py), or thiophene (Ar=Th) rings were synthesized by the Suzuki coupling reaction. Absorption maxima (λ_max) of HO-ArPh(m)-OHs shifted progressively toward long wavelengths due to the expansion of the π-conjugation system with an increase in the number of benzene rings. Deprotonation of the OH groups of HO-ArPh(m)-OHs by treatment with NaH caused a bathochromic shift of λ_max. The bathochromic shift of the deprotonated species increased with the donor numbers (DNs) of the solvents. The emission peak positions of NaO-ArPh(m)-ONas depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent.     

Ring Enlargement of Three-Membered Heterocycles by Treatment with In Situ Formed Tricyanomethane

Although the chemistry of elusive tricyanomethane (cyanoform) has been studied during a period of more than 150 years, this compound has very rarely been utilized in the synthesis or modification of heterocycles. Three-membered heterocycles, such as epoxides, thiirane, aziridines, or 2H-azirines, are now treated with tricyanomethane, which is generated in situ by heating azidomethylidene-malonodinitrile in tetrahydrofuran at 45 °C or by adding sulfuric acid to potassium tricyanomethanide. This leads to ring expansion with formation of 2-(dicyanomethylidene)oxazolidine derivatives or creation of the corresponding thiazolidine, imidazolidine, or imidazoline compounds and opens up a new access to these push–pull-substituted olefinic products. The regio- and stereochemistry of the ring-enlargement processes are discussed, and the proposed reaction mechanisms were confirmed by using ¹⁵N-labeled substrates. It turns out that different mechanisms are operating; however, tricyanomethanide is always acting as a nitrogen-centered nucleophile, which is quite unusual if compared to other reactions of this species.     

Triblock copolymers based on cyclic ethers: Preparation and properties of tetrahydrofuran and 3,3-bis(azidomethyl) oxetane triblock copolymers

Novel energetic thermoplastic elastomers (TPEs) based on tetrahydrofuran (THF) and 3,3-bis (azidomethyl) oxetane (BAMO) were prepared in this present study by cationic living polymerization. A bifunctional catalyst, triflic anhydride [(CF₃SO₂)₂)O] was selected to be an initiator for the polymerization THF and BAMO. The resulting polymers were characterized by IR, NMR, and DSC, which demonstrated that triblock copolymers with A-B-A type were formed. The polymers were indicated from thermogravimetric analysis (TGA) to have decomposed at approximately 243°C. The decomposition enthalpies were determined by DSC. These enthalpies were varied with the poly-BAMO contents of the copolymers. The synthesized polymers exhibited relatively good mechanical properties and thermoplastic characteristics at room temperature. © 1994 John Wiley & Sons, Inc.     

Cyclic (ALN)n Compounds as Precursors to Aluminum Nitride: Synthesis and Structure of [(CH3)2AlNH2]3 and the Planar Species [(t-C4H9)2AlNH2]3

Abstract

The crystal and molecular structures of the title compounds, [(CH₃)₂AlNH₂]₃ 1 and [(t-C₄H₉)₂AlNH₂]₃ 2, have been determined in connection with their investigation as possible precursors to aluminum nitride. Both compounds have an (AlN)₃ ring-structure with distorted tetrahedral geometries for the ring Al and N atoms. The distortion from tetrahedral geometry is most pronounced for the N atoms where the endocyclic Al-N-Al bond angles average 125.3 for 1 and 134.2 for 2. The (AlN)₃ ring in 1 is in a skew-boat conformation with no unusual intra- or intermolecular contacts. Compound 2 on the other hand exhibits an unprecedented planar (AlN)₃ ring as required by a crystallographic three-fold symmetry axis. The effects of the Al and N substituents on the (AlN)₃ ring size and conformation, as well as on the endocyclic Al-N-Al bond angles, are discussed in the context of the structural results obtained for these and other (AlN)_n ring compounds.