Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of β-hydroxythiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH4SCN in the presence of catalytic amount of a multi- site phase-transfer catalyst, α,α＇,α＂-N-hexakis（triethylammoniummethylene chloride）-melamine, is developed. A variety of ^-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times. 2009 Ali Reza Kiasat. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Zirconium triflate grafted on SBA-15 as a highly efficient solid acid catalyst for ring opening of epoxides by amines and alcohols

Metal(Al,Ti,Zr)triflate grafted mesoporous SBA‐15(AlTf/S,TiTf/S,ZrTf/S)samples were synthesizedas inexpensive solid acid materials by a simple one‐pot‐two‐step synthesis methodology.These materials were characterized by X‐ray diffraction,N2‐sorption,thermogravimetric analysis,Fourier transform infrared spectroscopy(FT‐IR),in‐situ pyridine FT‐IR spectroscopy,and elementalanalysis.ZrTf/S was found to be a highly efficient and reusable solid acid catalyst for ring opening ofepoxides with amines and alcohols and producedβ‐amino alcohols andβ‐alkoxy alcohols respectivelyunder ambient reaction conditions.The ZrTf/S catalyst showed the highest activity,whichwas attributed to its high acidity compared with that of the Ti and Al containing samples.

RING OPENING COPOLYMERIZATION OF SUCCINIC ANHYDRIDE-ETHYLENE OXIDE BY Al(Ⅲ) ORGANOMETALLIC CATALYSTS

Ring opening copolymerization of succinic anhydride (SA) with ethylene oxide (EO)was successfully carried out by using a series of aluminum-based catalyst in 1,4-dioxane at62±2℃. The results showed that in-situ AlR_3-H_2O (R=ethyl, iso-butyl) catalysts gavehigher molecular weight (M_w～10~4), while Al(OR)_3 catalysts gave the higher alternatingcopolymer structure with slightly lower molecular weight. The in-situ AlR_3-H_2O systemshave been evaluated in more detail for the reaction which showed the optimum H_2O/Almolar ratio to be 0.5. The copolymers with different composition (F_(SA)/F_(EO)= 36/64to 45/55 mol/mol) were synthesized by using different monomer feed ratio. The melt-ing point (T_m), glass transition temperature (T_g) and enthalpy of fusion (ΔH_f) of thesecopolymers are depended on the copolymer composition and in the range of 87～102℃,-12～-18℃, and 37～66J/g, respectively. The second heating scan of DSC also in-dicated that the higher alternating copolymer was more easily recrystallized. The onsetdecomposition temperature was more than 300℃ under nitrogen and influenced by thecopolymer composition.

Regio-and Diasteroselectivity of Rhodium-catalyzed Ring Opening Reaction of Oxabenzonorbornadienes with Heteroatom Nucleophiles

A new rhodium catalyzed ring opening reaction of oxabenzonorbornadienes and its derivatives was described. This reaction forms a new carbon-nitrogen bond via an intermolecular allylic displacement of the bridgehead oxygen with a piperazine's derivatives, which proceeds with very high regioselectivity.

Al(HSO_4)_3/silica gel as a novel catalytic system for the ring opening of epoxides with thiocyanate anion under solvent-free conditions

For the first time,metal hydrogen sulfates and phosphates/silica gel have been studied as efficient and powerful solid acid catalysts in the ring opening of epoxides with thiocyanate anion.The most significant result was obtained by Al(HSO4)3/SiO2which afforded the corresponding β-hydroxy thiocyanates under mild reaction conditions and in very short reaction times.The cheapness, availability of the catalyst,ease of procedure and work-up make this method attractive for the organic synthesis.

LIGAND EFFECT OF CATALYTIC SYSTEM WCl_6-Et_2Al FOR RING OPENING METATHESIS POLYMERIZATION OF DICYCLOPENTADIENE

Ligand effect of the catalytic system WCl6-Et2AlCl for ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) was investigated. The experimental results show that adding sterically hindered phenol-2. 6-di-tert-butylcresylol(DTBC) in the catalytic system not only can obviously increase the monomer conversion of polymerization but also improve the mechanical properties, such as notched impact strength (NIS), tensile strength (TS) ect. 5 of the synthesized polyicycolpentadiene (PDCPD). A similar effect can be observed by using a sterically hindered polymeric phenol - linear phenol formaldehyde resin (LPF) as a ligand.

TAILORING POLYMERS WITH NOVEL STRUCTURES VIA RING OPENING METATHESIS POLYMERIZATION

This paper reviewed some recent advances of ring opening metathesis polymerization (ROMP) in tailoring polymers with novel and controlled structures.

The Studies of Rhodium-catalyzed Ring Opening Reaction of N-Boc-azabenzonorbornadiene with Heteroatom Nucleophiles

A rhodium-catalyzed ring opening reaction of N-Boc-azabenzonorbornadiene with heteroatom nucleophiles was described. Piperidine and piperazine＇s derivatives were nucleophiles in this reaction. The yields of the products 2a-f are good and the regioselectivity are excellent.

Rhodium-catalyzed Asymmetric Ring Opening Reaction of Oxabenzo-norbornadiene with Substituted Phenolic Nucleophiles

We have developed an asymmetric ring opening reaction of oxabenzonorbornadienes with substituted phenolic nucleophiles. Under the reaction conditions （ [Rh（COD）C1]2 （1 mol%）, （S）-（R）-PPF-P^Bu2 （2 mol%）, THF, reflux）, the reaction products were obtained with high yield and enantiomeric excesses （ up to 99% ee）.

Rhodium-catalyzed asymmetric ring opening of azabenzonorbornadiene with substituted piperazine nucleophiles

We have developed an asymmetric ring opening reaction of azabenzonorbornadiene with substituted piperazine. By increasing the amount of catalyst (from 2.5 to 5%) and ligands (5 to 10%) as well as addition of ammonium iodide, the products can be obtained in high yield and the reaction time shortened dramatically, but the ee values were rather low.

A MILD AND REGIOSPECIFIC OXIRANE RING OPENING TO PRECURSORS FOR PROSTANOID CONGENERS

A stereoselective and regiospecific synthesis of procursors(2),(4),(6)and(7)of prostacyclin analogues from 2,3-epoxylbicyclo[3.2.0]hept-6-one(1)are described.

SYNTHESIS OF A COMB GRAFT COPOLYMER VIA RING OPENING METATHESIS POLYMERIZATION CATALYZED BY SUPPORTED RHUTHENIUM CARBENE COMPLEX

Chloromethyl-2-norbornene was synthesized via Diels-Alder reaction of cyclopentadiene and allyl chloride using a polymer supported boron trifluoride as the catalyst, and was then lithiated and used to initiate a living anionic polymerization of styrene to prepare a macromonome, 5-polystyryl-2-norbornene NBPS. Comb graft copolymer PNBgPS was synthesized via ring opening metathesis polymerization of the macromonomer under the catalysis of ruthenium carbene complex RuCl2(PPh3)2(=CCHtBu) and its polymer supported correspondent. Experimental results showed that the behavior of both the supported boron and supported ruthenium catalysts are superior to their unsupported counterparts. The possible promotion mechanism of the tailor-made supports is discussed.

The Oxirane Ring Opening of 2,3-endo-epoxybicyclo[3. 2 .0] hept-6-one by Amines at Alumina Surface

Stereospecific (trans) and regioselective nucleophilic opening of the title epoxide (I) by different amines at the alumina surface are described.

Solvent-Controlled Sc(OTf)_(3)-Catalyzed Ring Opening Reaction of 2-(Hetero)aryl-N-sulfonylazetidines:Synthesis of Allylic Amines/1,3-Oxazinane Derivatives

Allylic amines and 1,3-oxazinanes are valuable molecular skeletons in organic synthesis and pharmaceutical industry.A straightforward way to such two types of compounds by solvent-controlled rare-earth metal Lewis acid-catalyzed transformations of 2-(hetero)aryl-N-sulfonylazetidines:the ring-opening isomerization of azetidines to allylic amines and the annulation of azetidines with aldehydes to 1,3-oxazinanes are reported.These two reactions feature scalability,low catalyst loading,mild reaction conditions,excellent yields and regioselectivity with demonstrated utility in three-step product transformations to naftifine,abamine and abamine SG.

CATIONIC RING-OPENING POLYMERIZATION OF TETRAHYDROFURAN WITH KEGGIN-TYPE HETEROPOLYCOMPOUNDS AS SOLID ACID CATALYSTS

Three Keggin-type heteropolyanions, namely H3PMo12O40-13H2O, （NH4）3PMo12O40·4H2O and H3PW12O40·13H2O were prepared and tested in the ring-opening polymerization reaction of tetrahydrofuran. The effects of the counter-cation （H＋, NH4＋） and the peripheral atoms （Mo, W） on the polymerization were investigated. It has been found that when the protons of H3PMo12O40·13H2O were replaced by the ammonium cations the polymerization rate decreased dramatically. Whereas, when the peripheral atoms （Mo） were replaced by their homologous （W）, the polymerization rate increased twofold. As for the viscosity average molecular weight （My） of polymer products, it was found that the high molecular weight （7930） was obtained by using H3PW12O40·13H2O. The molecular weight （My） obtained by H3PMo12O40·13H2O and （NH4）H3PMo12O40·13H2O was 6470 and 6810, respectively.

Preparation of a highly efficient Pt/USY catalyst for hydrogenation and selective ring-opening reaction of tetralin

Ultrastable Y zeolite（USY）-supported Pt catalyst was prepared by gas-bubbling-assisted membrane reduction. The influence of reaction conditions and the metal and acid sites of catalysts on the catalytic performance of catalyst in hydrogenation and selective ring opening of tetralin, 1,2,3,4-tetrahydronaphthalene（THN）, was studied. It was found that the optimal reaction conditions were at a temperature of 280 °C, hydrogen pressure of 4 MPa, liquid hourly space velocity of 2 h^-1 and H2/THN ratio of 750. Under these optimal conditions, a high conversion of almost 100% was achieved on the 0.3 Pt/USY catalyst. XRD patterns and TEM images revealed that Pt particles were highly dispersed on the USY, favorable to the hydrogenation reaction of tetralin. Ammonia temperature-programmed desorption and Py-IR results indicated that the introduction of Pt can reduce the acid sites of USY, particularly the strong acid sites of USY. Thus, the hydrocracking reaction can be suppressed.

SYNTHESIS OF POLY(GLUTAMIC ACID-co-ASPARTIC ACID) VIA COMBINATION OF N-CARBOXYANHYDRIDE RING OPENING POLYMERIZATION WITH DEBENZYLATION

The random copolymers of glutamic acid （LG） and aspartic acid （ASP）, poly（LG-co-ASP）, with designed compositions could be successfully synthesized via combination of N-carboxyanhydride ring opening copolymerization with debenzylation. Ring opening copolymerizations of y：benzyl-L-glutamate N-carboxyanhydride （BLG-NCA） and β-benzyl-Laspartate N-carboxyanhydride （BLA-NCA） were carried out by using different amines including triethylamine （TEA）, diethylamine, n-hexylamine （NHA）, triphenylamine, diphenylamine or aniline as initiators. All the 6 amines were highly efficient to get well-defined poly（BLG-co-BLA） copolymers with designed compositions although the polymerizations proceeded via different mechanisms （normal amine mechanism or/and activated monomer mechanism）, which are based on chemical structure of amines. The molecular weights of poly（BLG-co-BLA） copolymers could be mediated by both TEA concentration and polymerization time. Then, debenzylation ofpoly（BLG-co-BLA） copolymers was conducted to prepare the corresponding hydrophilic random eopolymers of poly（LG-co-ASP） with a-subunit structure in ASP structural units. The contents of LG structural units in poly（LG-co-ASP） copolymers matched with those of BLG-NCA in NCA-monomer feeds in ring opening copolymerizations initiated by NHA or TEA and were closed to the theoretical line. The diblock copolymer of poly（BLG-b-BLA） could also be synthesized via living NCA ring opening copolymerization by sequential addition of BLG- NCA and BLA-NCA.

Sidearm as a Control in the Asymmetric Ring Opening Reaction of Donor-Acceptor Cyclopropane

A new type of trisoxazoline and bisthiazoline based ligands have been developed,which are absent of chiral motif on the parent skeleton and containa chiral backbone on sidearm.The ligands promote the amine nucleophilic ring opening reaction of 1,1-cyclopropane diesters smoothly,furnishing the γ-amino acid derivatives in high yield with moderate to good enantioselectivity.

Controlled Random Terpolymerization of β-Propiolactone,Epoxides,and CO_(2) via Regioselective Lactone Ring Opening

The random ring-opening terpolymerization of CO_(2),epoxides,and lactones remains challenging,mainly because CO_(2)/epoxide copolymerization and lactone ring-opening polymerization typically proceed at very different rates.Herein,we report the preparation of novel statistical terpolymers with random distributions of carbonate and ester units(up to 40%junction units)via the one-pot reaction ofβ-propiolactone(BPL),epoxides,and CO_(2) under mild conditions using a binary catalyst system consisting of SalcyCo(III)OTs(Salcy=N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane;OTs=p-toluenesulfonate)and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.Since this catalytic system could yield similar reaction rates for alternating epoxide/CO_(2) copolymerization and BPL polymerization,terpolymers with nearly identical compositions were produced at various time points.CO_(2) played an important role in preventing intra-and/or intermolecular transesterification side reactions.Thereby,the terpolymerization proceeded in a controlled manner,allowing for the fine-tuning of molecular weight and composition.Two-dimensional nuclear magnetic resonance(NMR)analysis and density functional theory(DFT)calculations suggested that the nucleophilic attack of the coordinated BPL by carbonate ions cleaved the alkyl C–O bond predominantly rather than the acyl C(=O)–O bond,typically observable during the nucleophilic ring-opening polymerization of BPL.These findings have opened up a new avenue for preparing a broad family of biodegradable polymers with adjustable properties.

Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides by Aromatic Amines

Silica chloride nano particle （nano SiO2-C1）, has been found to be heterogeneous catalyst for facile, simple and mild ring opening of epoxides with aromatic amines to afford β-amino alcohols in dry CH2C12 at room temperature.