立构规整性二氧化碳共聚物:从无定型到结晶性材料转变

二氧化碳与环氧烷烃交替共聚制备降解性聚碳酸酯是重要的绿色聚合反应之一.尽管二氧化碳共聚物的工业化已经具备了一定基础,但却受制于材料性能、品种单一等问题,发展十分缓慢.先前发展的二氧化碳基聚碳酸酯是非晶且玻璃化转变温度较低,存在高温强度迅速变差等问题.通过立构规整性聚合使碳酸酯单元在主链上有序排列可能是该类聚合物结晶的主要途径.本文重点介绍了二氧化碳与环氧烷烃的立构规整性聚合方面的最新研究进展,包括高立构规整性催化剂的设计,以及结晶性二氧化碳基聚碳酸酯的创制工作.     

General,Highly Selective Synthesis of 1,3‐ and 1,4‐Difunctionalized Building Blocks by Regiodivergent Epoxide Opening

We describe a regiodivergent epoxide opening (REO) featuring a catalyst‐controlled synthesis of enantiomerically and diastereomerically highly enriched or pure syn‐ and anti‐ 1,3‐ and 1,4‐difunctionalized building blocks from a common epoxide precursor. The REO is attractive for natural product synthesis and as a branching reaction for diversity‐oriented synthesis with epoxides.     

Amphiphilic perfluoroalkylated sulfones and sulfonate betaines

Two types of perfluoro alkyl-containing amphiphilic sulfones 7-9 and 13-15, respectively, and sulfonate betaines 23-32 were prepared using 2-[(perfluoroalkyl)methyl]oxiranes (1-3, R_F = C₄F₉, C₆F₁₃, C₈F₁₇) or 3-(perfluoroalkyl)propyl iodides (16 and 17, R_F = C₆F₁₃, C₈F₁₇) as the starting compounds. The overall yields of two-step syntheses were above 90%. The compounds 7-9 were prepared by the reaction of oxiranes 1-3 with 2-sulfanylethan-l-ol and subsequent oxidation of intermediate sulfides. Similarly, the amphiphiles 13-15 were obtained by analogous reaction of oxiranes 1-3 with thiomorpholine and subsequent oxidation of the sulfur atom in the morpholine ring. In the syntheses of betaines 23-32, the starting compounds 1-3 or 16 and 17 were first reacted with dimethylamine followed by the ring-opening reaction of the intermediate fluoroalkyl(dimethyl)amines with propane-1,3- or butane-1,4-sultones.     

SN2 Reactions at Tertiary Carbon Centers in Epoxides

Described herein is a novel concept for S_N2 reactions at tertiary carbon centers in epoxides without activation of the leaving group. Quantum chemical calculations show why S_N2 reactions at tertiary carbon centers are proceeding in these systems. The reaction allows flexible synthesis of 1,3‐diol building blocks for natural product synthesis with excellent control of the relative and absolute configurations.     

Construction of bicyclic systems containing an oxygen bridge by isomerization of cyclic epoxy alcohols

A novel method for constructing a 7-oxabicyclo[2.2.1]heptane skeleton was developed. The substrates, namely cis-3,4-epoxy-1-cyclohexanol derivatives, were prepared from the corresponding 3-cyclohexen-1-ol derivatives via a stereoselective epoxidation reaction using a vanadium catalyst. Upon heating with lithium iodide in propionitrile, the cis-epoxy alcohol was transformed into the 7-oxabicyclo[2.2.1]heptane derivative in high yield. The reaction proceeds through formation of a lithium alkoxide bearing an iodohydrin moiety, followed by an intramolecular S_N2 reaction.     

Ultrasonic activated efficient method for the cleavage of epoxides with aromatic amines

An improved protocol for the cleavage of epoxides with aromatic amines in the presence of FeCl₃ promoted by ultrasonic irradiation. This new methodology provides excellent yields in short reaction times (15–25 min) at room temperature.     

Asymmetric Total Synthesis of Stagonolide G

A simple asymmetric total synthesis of stagonolide G ( 1 ) is described. Asymmetric dihydroxylation, regioselective epoxide ring opening, and vinyl Grignard reactions are involved in generating the stereogenic centers C(4) and C(8), followed by Grubbs‐II‐catalyzed ring‐closing metathesis (RCM).     

Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14-74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core-shell structures with CNTs at the center.     

Convenient synthesis of 5-aryl(alkyl)sulfanyl-1,10-phenanthrolines from 5,6-epoxy-5,6-dihydro-1,10-phenanthroline, and their activity towards fungal β-d-glycosidases

A broad series of novel 5-aryl(alkyl)sulfanyl-1,10-phenanthrolines has been prepared by a new simple procedure: a treatment of the commercially available 5,6-epoxy-5,6-dihydro-1,10-phenanthroline with various thiols in the presence of a base. Other functional groups attached to the thiol allow a use of the products as building blocks in synthesis of versatile ligands and in functionalization of surfaces. The synthesized phenanthrolines showed a moderate ability as activators or inhibitors of fungal β-d-glucosidases and β-d-galactosidases.     

Oxidation reactions using polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine

A thermally stable polymer-supported oxidant has been developed. Polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine was applied to microwave-assisted reactions that occurred at high temperatures and was shown to oxidize alkenes, silyl enol ethers, and pyridines to the corresponding epoxides and pyridine N-oxides in excellent to good yields and with much shorter reaction times. It also enabled tetrahydrobenzimidazoles to be oxidatively rearranged to spiro fused 5-imidazolones in a more efficient manner. Recycling of the polymer-supported oxidant is also possible with minimal loss of activity after several reoxidations.