Femto/Picosecond Transient Absorption Study of Ring-Opening Dynamics in Perimidinespirocyclohexadienone Derivatives

The ring-opening dynamics of perimidinespirocyclohexadienone derivatives has been studied by means of time-resolved spectroscopy in cyclohexane and acetonitrile solutions. It has been established that molecular isomerisation leading to the open isomer occurs against the background of the S₁-S₀ internal conversion of the cyclic form. In addition, the features of the observed spectral changes in the cyclohexane made it possible to distinguish formation of the photoproduct in the T₁ state and its relaxation via intersystem crossing to the singlet ground state. The corresponding assignments for transient absorption bands were performed on the basis of TD-DFT calculations.     

Asymmetric ring-opening reaction of azabenzonorbornadienes with phenols promoted by palladium/(R,R)-DIOP complex

An efficient asymmetric ring opening reaction of azabenzonorbornadienes with various phenols using Palladium/(R,R)-DIOP complex has been demonstrated, the reaction afforded the corresponding products in excellent yields (80–95%) with moderate enantioselectivities (50–64% ees). The syn-configuration of the product was confirmed by the single X-ray crystallography.     

Dipolar cycloadditions of imidazoline 3-oxides with N-arylmaleimides. Synthesis and diethylamine induced ring-opening of exo and endo hexahydro-7-oxa-2,5,6a-triaza-cyclopenta[a]pentalene-1,3-diones

1,4-Diarylimidazoline 3-oxides react with N-arylmaleimides in benzene to give predominantly the corresponding endo adducts. Chiral imidazoline 3-oxides react diastereospecifically (cis configuration of the tetrahydroimidazo ring) and diastereoselectively to give cis-endo adducts. The effects of substituents on the aromatic ring of the maleimide was investigated. The presence of electron-withdrawing or releasing groups have minor effect on the total yields but more pronounced is the effect on the ratio of exo and endo diastereomers. The adducts undergo an interesting and unprecedented ring-opening in the presence of secondary amines to give deoxygenated 3-imidazoline 3-oxides instead of the expected double cis elimination products. Tertiary amines did not induce any reaction.     

Synthesis of L-Aspartic Acid and Lactone Copolymers

Recently,thesynthesisandapplications0fbiodegradablepolydepsipeptides,alternatingcopolymersofa-aminoacidanda-hydroxyacidwithfunctionalside-chaingroupshavedrawnmoreandmoreattentionl'2.Thisisbecausethefunctionalizedpendantgroups0fthep0lydepsipeptidesmakethemusefulf0rthepreparationofavarietyofpolymer-drugconjugates.However,thepolymerizati0nofdepsipeptideswithfuncti0nalgr0upsisratherdifficultduetotheirbigstructuresandsterichindrance.Furthermore,high-molecular-weightpr0ductsofsuitablephysicalpropert…     

新型含酯基的可生物降解聚碳酸酯的合成

通过2，2-二羟甲基-丙二酸二甲酯与氯甲酸乙酯的反应合成了环状碳酸酯单体5，5-二甲氧羰基-1，3-二氧六环-2-酮，再以异辛酸亚锡为催化剂，在不同温度下进行本体开环聚合，得到新型含酯基的聚碳酸酯．单体和聚合物结构经红外光谱(IR)、核磁共振氢谱(1^H NMR)及核磁共振碳谱(^12C NMR)表征．结果表明，开环聚合反应的产率和分子量随温度的升高而增加，但温度高于100℃时开环聚合会发生一定程度的脱羧反应，研究得出该聚合反应合适的反应条件为：反应温度90℃，反应时间12h，聚合过程中基本无脱羧反应发生。     

Characterization of the benzene-insoluble fraction of the hydrolyzate of phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide

The insoluble fraction obtained from the hydrolysis and condensation of (4-dimethylamino-, 2-methyl-, and nonsubstituted)phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide in benzene was characterized. IR, ¹H NMR, and ²⁹Si NMR suggested that the insoluble fraction was composed of RSi(O )₃, that is, a T³ structure. X-ray diffraction indicated the presence of a long-range ordered structure composed of a mixture of crystals. Raman spectroscopy strongly suggested a cage structure by the presence of a ring-opening vibration assignable to a cubic structure at 475–482 cm⁻¹. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4587–4597, 2004     

开环聚合制备高分子量聚二茂铁衍生物及其性能的研究

综述了近年来国内外高分子量聚二茂铁衍生物的研究进展。对热引发、阴离子引发、过渡金属催化等开环聚合方法及机理以及聚合物结构、性能及潜在应用作了介绍。     

Recent Advances in Ring‐Opening Functionalization of Cycloalkanols by C–C σ‐Bond Cleavage

Cycloalkanols prove to be privileged precursors for the synthesis of distally substituted alkyl ketones and polycyclic aromatic hydrocarbons (PAHs) by virtue of cleavage of their cyclic C−C bonds. Direct functionalization of cyclobutanols to build up other chemical bonds (e. g., C−F, C−Cl, C−Br, C−N, C−S, C−Se, C−C, etc.) has been achieved by using the ring‐opening strategy. Mechanistically, the C−C cleavage of cyclobutanols can be involved in two pathways: (a) transition‐metal catalyzed β‐carbon elimination; (b) radical‐mediated ‘radical clock’‐type ring opening. The recent advances of our group for the ring‐opening functionalization of tertiary cycloalkanols are described in this account.     

Selective Polymerization Catalysis from Monomer Mixtures: Using a Commercial Cr‐Salen Catalyst To Access ABA Block Polyesters

ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone. The catalysis is highly selective and applies a single catalyst in two distinct pathways. It occurs first by epoxide/anhydride ring‐opening copolymerization and subsequently by lactone ring‐opening polymerization. It is used to produce various new ABA polyester polyols; these polyols can undergo post‐functionalization and chain‐extension reactions. The ability to use a commercial catalyst and switchable catalysis with monomer mixtures is expected to facilitate future explorations of new classes of block polymers.