Ring Opening Of THF Research Articles

Revisited Synthesis of Trispyrazolylborate Aluminum Halides Suban Kundu, Raju Chambenahalli, Alex P. Andrews and Ajay Venugopal*

Tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2 (X=Cl, Br and I) can be potential precursors for preparing highly electrophilic dications as well as low oxidation state aluminum compounds. However, the coordinative unsaturation in TpMe2AlX2 makes them susceptible to rearrangement to [Tp2Al][AlX4]. In this work, we revisited the synthesis of TpMe2AlX2 by isolating the solvent‐stabilized tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2(L) (X=Cl, Br; L = THF, HPMA). Efforts to isolate TpMe2All2 resulted in the ring opening of THF revealing the mediation of a highly reactive cationic aluminum species. The monocationic, [TpMe2AlCl(THF)2][B{C6H3(CF3)2}4] was prepared from TpMe2AlCl2(THF) via silver salt metathesis. Attempts to prepare the dicationic species [TpMe2Al(THF)3]2+ resulted in the instantaneous ring‐opening polymerization of THF.

Alkane Elimination Preparation of Heterobimetallic MoAl Tetranuclear and Binuclear Complexes Promoting THF Ring Opening

We report a straightforward alkane elimination strategy to prepare well-defined heterobimetallic Al/Mo species. Notably, the reaction of the monohydride complex of molybdenum, Cp*MoH(CO)3, with triisobutyl aluminum affords a new heterobimetallic [MoAl]2 tetranuclear compound, [Cp*Mo(CO)(µ-CO)2Al(iBu)2]2, (1), featuring a 12-membered C4O4Mo2Al2 ring in which isocarbonyls bridge the Mo and Al centers. The addition of pyridine to this complex successfully results in the dissociation of the dimer into a new discrete binuclear complex, [Cp*Mo(CO)2(µ-CO)Al(Py)(iBu)2], (2). Switching the nature of the Lewis base from pyridine to tetrahydrofuran does not lead to the THF analogue of adduct 2, but rather to a complex reaction where one of the identified products corresponds to a tetranuclear species, [Cp*Mo(CO)3(μ-CH2CH2CH2CH2O)Al(iBu)2]2, (3), featuring two bridging alkoxybutyl fragments originating from the C-O ring opening of THF. Compound 3 adds to the unusual occurrences of THF ring opening by heterobimetallic complexes, which is evocative of masked metal-only frustrated Lewis pair behavior and highlights the high reactivity of these Al/Mo assemblies.

Structure and spectroscopic properties of etherates of the beryllium halides

Abstract The synthesis of beryllium halide etherates and the solution behavior in benzene, dichloromethane, and chloroform was studied by NMR, IR, and Raman spectroscopy. Mononuclear units of [BeX 2(L)2] (X = Cl, Br, I; L = Et2O, thf) were identified as the favorably formed species in solution. Treatment of the mononuclear diethyl ether beryllium halide adduct with one equivalent beryllium halide formed the dinuclear compounds [BeX 2(OEt2)]2 (X = Cl, Br, I). The solid-state structures of [BeCl2(thf)2] and [BeBr2(thf)2] have been determined by single crystal X-ray diffraction analysis. [BeI2(thf)2] decomposed in all solvents. In CD2Cl2 the salt [Be(thf)4]I2 was formed, whereas in C6D6 and CDCl3, BeI2 precipitated and [BeI(thf)3]+, [Be(thf)4]2+ together with the thf ring-opening product [Be(μ 2-O(CH2)4I)I(thf)]2 were observed in solution.

Poly(dithiophosphate)s, a New Class of Phosphorus- and Sulfur-Containing Functional Polymers by a Catalyst-Free Facile Reaction between Diols and Phosphorus Pentasulfide.

Novel poly(dithiophosphate)s (PDTPs) were successfully synthesized under mild conditions without any additive in the presence of THF or toluene diluents at 60 °C by a direct, catalyst-free reaction between the abundant phosphorus pentasulfide (P4S10) and glycols such as ethylene glycol (EG), 1,6-hexanediol (HD) and poly(ethylene glycol) (PEG). GPC, FTIR, 1H and 31P NMR analyses proved the formation of macromolecules with dithiophosphate coupling groups having P=S and P-SH pendant functionalities. Surprisingly, the ring-opening of THF by the P-SH group and its pendant incorporation as a branching point occur during polymerization. This process is absent with toluene, providing conditions to obtain linear chains. 31P NMR measurements indicate long-time partial hydrolysis and esterification, resulting in the formation of a thiophosphoric acid moiety and branching points. Copolymerization, i.e., using mixtures of EG or HD with PEG, results in polymers with broadly varying viscoelastic properties. TGA shows the lower thermal stability of PDTPs than that of PEG due to the relatively low thermal stability of the P-O-C moieties. The low Tgs of these polymers, from -4 to -50 °C, and a lack of PEG crystallites were found by DSC. This polymerization process and the resulting novel PDTPs enable various new routes for polymer synthesis and application possibilities.

Difluorocarbene‐Induced Ring Opening of Tetrahydrofuran with TMSCF2Br for Difluoromethoxybutylation of N‐Aryl‐N‐hydroxylamines

AbstractIn this work, a novel difluorocarbene‐induced ring opening of THF with TMSCF2Br for difluoromethoxybutylation of N‐aryl‐N‐hydroxylamines under mild conditions is reported. The mechanism study revealed that THF was intermolecular activated by difluorocarbene, then the formed oxonium ylide was nucleophilic attacked by N‐aryl‐N‐hydroxylamines.

The first total synthesis and revision of absolute stereochemistry of natural cytotoxic lactone cleistanolate

Development of a synthetic route applicable to d-ribose and d-xylose enabled the synthesis of cleistanolate putative structure, its five stereoisomers, and led to revision and confirmation of absolute stereochemistry of the natural product. Key steps of the synthesis included zinc-mediated THF ring-opening and stereoselective dihydroxylation under the Upjohn conditions. The first total synthesis of cleistanolate was completed in eight steps starting from d-xylose. The C-5 stereocenter of the natural product was assigned the correct (5S)-stereochemistry. Cytotoxicity of natural product was briefly investigated.

Ring-Opening of THF via an Intramolecular P/Al-Based Frustrated Lewis Pair: Assistance by C6F5 Groups beyond Electronegativity?

Ring-Opening of THF via an Intramolecular P/Al-Based Frustrated Lewis Pair: Assistance by C₆F₅ Groups beyond Electronegativity?

Asymmetric synthesis and biological evaluation of (+)-cardiobutanolide, (−)-3-deoxycardiobutanolide and analogues as antiproliferative agents

Two natural products, (+)-cardiobutanolide and (−)-3-deoxycardiobutanolide, as well as five new analogues, were synthesized in several steps that included zinc-mediated THF ring opening, subsequent stereoselective olefination, and final Sharpless asymmetric dihydroxylation. In vitro antitumour activities of these compounds were evaluated against a panel of eight human tumour cell lines and one normal cell line. Some of compounds displayed powerful effects against tumour cells, but none of them were active toward normal cells. A SAR study revealed that the change of configuration at the C-6 and C-7 position of (+)-cardiobutanolide decreases antitumour activity of analogues. It also appears that the presence of a hydroxyl group at the C-3 position increases the activity of this type of lactones. A comparison of activities of conformationally rigid lactone goniofufurone with that of more flexible cardiobutanolide and 3-deoxycardiobutanolide indicates that steric flexibility has a positive effect on cytotoxicity. It was also confirmed that removal of the phenyl group may result in analogues of higher activity. Flow cytometry analysis revealed that the synthesized compounds did not induce apoptosis and necrosis of K562 cells. However, Western blot analysis showed that all compounds but one had an increased Bax/Bcl-2 protein expression ratio.

A Stable Naked Dithiolene Radical Anion and Synergic THF Ring-Opening.

Reaction of the lithium dithiolene radical 2• with the imidazolium salt [{(Me)CN(i-Pr)}2CH]+[Cl]- (in a 1:1 molar ratio) gives the first stable naked anionic dithiolene radical 3•, which, when coupled with hexasulfide, [{(Me)CN(i-Pr)}2CH]+2[S6]2- (4), and N-heterocyclic silylene 5, unexpectedly results in synergic THF ring-opening via a radical mechanism.

Asymmetric synthesis of the cytotoxic lactone (+)-cardiobutanolide and two novel analogues

A new asymmetric synthesis of the naturally occurring styryl lactone cardiobutanolide and two novel analogues have been achieved starting from d-xylose. The key steps of the synthesis included an initial zinc mediated reductive THF-ring opening, stereoselective olefination and Sharpless asymmetric dihydroxylation. It was shown that cardiobutanolide (1) exhibits promising in vitro antitumour properties against certain human neoplastic cell lines. It was more potent than the commercial anticancer agent doxorubicin against three cell lines (K562, HL-60 and Raji).

A Sequential One‐Pot Synthesis of Functionalized Esters and Thioesters through a Ring‐Opening Acylation of Cyclic Ethers and Thioethers

A one‐pot protocol for the synthesis of functionalized esters and thioesters is reported from cyclic ethers/thioethers and carboxylic acids via acyloxyphosphonium salts as key intermediates. The reaction of styrene oxide with acyloxyphosphonium salts gave complete regioselectivity and good yields of the resulting functionalized ester, whereas cyclohexene oxide gave moderate yields. Styrene episulfide, on the other hand, gave good yields with moderate regioselectivity whereas cyclohexene sulfide gave quantitative yields of the corresponding thioesters. We have also shown an alternate procedure for the ring opening of THF to form 4‐bromo butyl esters. All these reactions were carried out in the absence of a catalyst, showing the synthetic versatility of our method.

4-(Ph3 B)-2,6-Mes2 Py]- : A Sterically Demanding Anionic Pyridine.

The introduction of a triphenylborate group at the 4-position of 2,6-dimesitylpyridine afforded a sterically demanding anionic pyridine. The charge introduced through the borate group drastically increases its basicity and measurement of its pKa value (18.46) revealed a significantly higher value than that of 4-dimethylaminopyridine (17.95). THF ring-opening was observed upon treating its lithium salt with TMSCl, which demonstrates its high nucleophilicity. The mesityl groups at the 2,6-positions are oriented orthogonal to the pyridine ring and do not block the nitrogen atom of the pyridine. The reaction of the protonated pyridine with Li[BH4 ] yielded the corresponding Lewis acid/base adduct, which shows that the title compound can be used as a monodentate ligand in coordination chemistry. The crystal structures of all the compounds presented in this work are reported.

A DFT Study on the Mechanism of the FLP-access to N-Arylazacycles from Cyclic Ethers: Sequential Activation of Two C–O Bonds

Computational studies suggested that the B(C6F5)3-catalyzed synthesis of N-arylpyrrolidines from arylamines and cyclic ethers was achieved via two consecutive C–O bond activation steps by the generation of a frustrated Lewis pair. The formation of the Lewis acid–base adduct between B(C6F5)3 and THF was crucial in the ring opening of THF while the existence of FLP was also indispensable in the cyclization process.

One-pot synthesis of imidazolinium salts via the ring opening of tetrahydrofuran.

A new one-pot synthesis of C2-hydroxypropyl-substituted imidazolinium salts via the ring opening of tetrahydrofuran (THF) with N,N'-disubstituted diamines has been developed. Preliminary studies of the reaction mechanism suggest the CO2-promoted oxidative ring opening of THF followed by Hg(ii)-mediated oxidation of an imidazolidine intermediate. These novel C2-substituted imidazolinium salts have shown to be active catalysts for the aza-Diels-Alder reactions.

Ring-opening of cyclic ethers by aluminum hydridotriphenylborate.

Molecular aluminum hydride [(L)AlH2] (L = Me3TACD) reacted with 2 equiv. of BPh3 in THF or THP to give the cationic alkoxides [(L)Al(OR)][HBPh3] (R = nBu, nPent) by facile ring-opening of the cyclic ethers. The Cα-O bond cleavage which involves the isolable intermediate [(L)AlH][HBPh3] is a result of hydride transfer to Cα from [HBPh3]-.

Facile ring-opening of THF at a lithium center induced by a pendant Si-H bond and BPh3.

The macrocyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane [LH = (Me3TACD)H] formed adducts with tetramethyl-silazides [M{N(SiHMe2)2}] (M = Li, Na, K) of light alkali metals. Upon heating, intramolecular dehydrocoupling occurred to give [M{(L)SiMe2N(SiHMe2)}]. BPh3 induced facile ring-opening of THF when reacted with [Li{(L)SiMe2N(SiHMe2)}].

ChemInform Abstract: Magnesium Halide‐Promoted Ring‐Opening Reaction of Cyclic Ether in the Presence of Phosphine Halide.

A new route to the direct preparation of H-phosphinate esters has been explored. The ring-opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl2 or PCl3). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide-mediated THF ring-opening (SN2@C) and the subsequent SN2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings (Path I: SN2@C−+SN2@P). Another possible route, the direct SN2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide (Path II: SN2@P−+SN2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H-phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX2 in protic solvents like water, MgBr2 is recommended for ring-opening reactions of cyclic ethers.

A Comparative Study of AlCl3and FeCl2-Modified TiCl4/MgCl2/THF Catalytic System in the Presence of Hydrogen for Ethylene Polymerization

Ethylene homopolymerization over TiCl4/MgCl2/THF catalysts modified with different metal halide additives (AlCl3and FeCl2) with and without hydrogen was investigated based on catalytic activity and polymer properties. Lewis acid modification can improve activity because it can remove the remaining THF in the final catalyst, which can poison the catalyst active sites via the ring-opening of THF that was confirmed by XRD measurements. Moreover, the activity enhancement was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Thus, FeCl2doped catalyst (Fe-THF) exhibited the highest activity followed by AlCl3doped catalyst (Al-THF) and undoped catalyst (None-THF). In H2/C2H4molar ratio of 0.08, Fe-THF showed a better hydrogen response than Al-THF due to more titanium cluster distribution. Fe-THF is considered to have more clustered Ti species than Al-THF. As a consequence, it led us to obtain more possible chances to precede chain transfer reaction by hydrogen. The molecular weight, melting temperature, and crystallinity of obtained polymers were investigated by GPC and DSC measurement, respectively.

Sterically induced reductive linkage of iron polypnictides with bulky lanthanide complexes by ring-opening of THF.

Reduction of [Cp*Fe(η5-E5)] (E = P, As) with divalent lanthanide reagents usually leads to reduction of [Cp*Fe(η5-E5)] followed by a Ln-E bond formation. In contrast, by using the sterically encumbered reagent [(DippForm)2Sm(thf)2] (DippForm = {(2,6-iPr2C6H3)NC(H)[double bond, length as m-dash]N(2,6-iPr2C6H3)}-), ring-opening of thf and reduction of the polypnictide is observed. This leads to two new 3d/4f polyphosphide or polyarsenide complexes [(DippForm)2Sm(Cp*Fe)E5{(CH2)4O}{(DippForm)2Sm(thf)}], in which [(DippForm)2Sm(thf)2] and [Cp*Fe(η5-E5)] are linked by a ring-opened thf molecule and no Ln-E bond formation is observed.

Magnesium Halide‐promoted Ring‐opening Reaction of Cyclic Ether in the Presence of Phosphine Halide

AbstractA new route to the direct preparation of H‐phosphinate esters has been explored. The ring‐opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl2 or PCl3). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide‐mediated THF ring‐opening (SN2@C) and the subsequent SN2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings (Path I: SN2@C−+SN2@P). Another possible route, the direct SN2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide (Path II: SN2@P−+SN2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H‐phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX2 in protic solvents like water, MgBr2 is recommended for ring‐opening reactions of cyclic ethers.