Microwave-assisted aminolysis of vinylepoxides

Di- and trisubstituted vinylepoxides in NH₄OH were subjected to microwave irradiation affording the corresponding vicinal aminoalcohols in high yields. The reaction is stereospecific and highly regioselective for addition at the allylic carbon.     

Synthesis and structural characterisation of the oxo-rhenium(V) complexes with spirophosphorane derived bidentate ligand (PO). Crystal structure of trans-ReOCl2[OCMe2CMe2OP(OCMe2CMe2O)](PPh3)

The reactions of ReO(OEt)Cl₂L₂, L=py, PPh₃ or ReOCl₃(Me₂S)(OPPh₃), with spirohydrophosphorane HP(OCMe₂CMe₂O)₂ – abbreviated here as HPO – in toluene yield ReOCl₂(PO)L complexes, L=py (1), PPh₃ (2) and OPPh₃ (3), respectively. The encountered bidentate phosphite pinacolato (OCMe₂CMe₂O)POCMe₂CMe₂O⁻ ligand (PO⁻) is afforded by means of a spirophosphorane ring-opening reaction. All the pink–violet compounds 1–3 were characterised by NMR, IR and UV–Vis spectroscopies. The structure of trans-ReOCl₂(PO)PPh₃ (2) was determined crystallographically. The rhenium atom adopts distorted octahedral geometry with a trans multiply bonded terminal oxo ligand (Re–O_t=1.698(2) Å) trans to pinacolate oxygen (Re–O=1.880(2) Å). Two phosphorus atoms as well as two chlorides are mutually in a trans arrangement.     

Star-shaped fluorescent polypeptides

Two series of novel, four-arm, star-shaped polypeptides were prepared via the ring-opening polymerization of γ-benzyl-L -glutamate N-carboxyanhydride and ϵ-benzyloxycarbonyl-L -lysine N-carboxyanhydride with a tetra-amino-substituted perylene fluorophore as the initiator. The removal of the α-amino acid side-chain-protecting groups resulted in unprecedented water-soluble, perylene-functionalized, star-shaped polypeptides that showed strong fluorescence in aqueous solution. One of the features that distinguished these water-soluble star polypeptides from most other star polymers was that the conformation of the arms could be reversibly changed from a random coil into an α helix by variations in the pH of the aqueous solution. These star polypeptides might be of interest for the development of novel fluorescent probes or as traceable, stimuli-sensitive molecular containers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1572–1583, 2001     

Influence of polymerization conditions on the molecular weight and polydispersity of polyepichlorohydrin

The influence of the relevant reaction conditions on the molecular weight and polydispersity during the cationic ring-opening polymerization of epichlorohydrin has been studied using an experimental design. The polymerization was conducted in the presence of an alcohol (diol and triol), a Lewis acid at two temperatures (5 °C and 25 °C), and with two monomer addition rates. FT-IR spectra were used for the chemical characterization of the polymer, and MALDI-TOF mass spectrometry was used to determine the oligomeric composition and the masses of the initiator or transfer agent. The FT-IR showed the characteristic peaks of polyepichlorohydrin, and the mass spectra indicate that the alcohol was incorporated in the polymer structure. The MW and polydispersity were determined using gel permeation chromatography. We observed that the two most significant parameters that affected MW were the monomer addition rate and the reaction temperature, whereas polydispersity was most strongly affected by the monomer addition rate.     

Synthesis of the C42-C52 part of ciguatoxin CTX3C

The C42-C52 part of ciguatoxin CTX3C (1) was synthesized from tri-O-acetyl d-glucal. The synthetic segment had a tetrahydropyran ring corresponding to the ‘C49-reduced’ L-ring of 1, designed to avoid side reactions due to acid-labile C49 acetal carbon during acidic reductive conditions planned in further synthesis toward 1. The vicinal dimethyl part at C47-C48 was constructed by a stepwise conjugate addition/methylation procedure. The C50-C52 unit was installed by Grignard addition of the C₃ unit followed by spirocyclization and reductive cleavage of the spirocyclic acetal. Stereoselective assembly of the C42-C44 part was achieved by Brown’s asymmetric crotylboration.     

New High-Performance Catalysts Developed at Mitsui Chemicals for Polyolefins and Organic Synthesis

This contribution reports Mitsui's R&D activities in the field of catalysis technology focusing on molecular catalysts. Examples of the high-performance molecular catalysts developed at Mitsui include bis(phenoxy-imine) group 4 transition metal complex catalysts (FI Catalysts), phosphazene catalysts (PZN catalysts) and b(beta)-ketoiminato Co(II) complex catalysts. Many of the materials stemming from these catalysts were either difficult or impossible to prepare using conventional catalysts.     

(Salen)Ti(IV)-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

As an important strategy for the formation of 1,2-bifunctionalized systems theasymmetric ring-opening of epoxides with different nucleophiles has drawn muchattention from the organic chemists. A wide variety of nucleophiles are utilized in theaforemention…     

三（3,5-二叔丁基水杨醛缩苯乙胺）镧引发ε-己内酯开环聚合研究

首次采用三（3,5-二叔丁基水杨醛缩苯乙胺）镧[La（OPEBS）3]作为单组份引发剂用于引发ε-己内酯（ε-CL）的开环聚合.系统研究了溶剂、反应温度、单体/引发剂比例、单体浓度和反应时间对聚合反应的影响.研究结果表明La（OPEBS）3具有很高的催化活性,可以在反应温度为40℃,[-εCL]/[La]摩尔比为1 000,反应时间为40 min的聚合条件下得到分子量约为5.84×104,产率为99.9%的聚己内酯（PCL）.1H NMR结果显示己内酯单体是通过酰-氧键的断裂插入增长链.     

Thermodynamic and Kinetic Polymerizability of Cyclic Esters

Recent advances in the controlled ring-opening polymerization (ROP) of cyclic aliphatic esters are reviewed with a particular attention to thermodynamics and kinetics of the polymerization of industrially important monomers, namely: lactide (LA), 1,4-dioxan-2-one (DX), and ϵ-caprolactone (CL). For comparison, polymerization of β-lactones is discussed. Progress in stereocontrolled polymerization of monomers bearing centers of chirality [LA and β-butyrolactone (BL)] is also briefly reviewed.