Synthesis of a triphenylphosphine reagent on non-cross-linked polystyrene support: application to the Staudinger/Aza-wittig reaction

A new triphenylphosphine reagent linked to a linear polystyrene was synthesized. The reactivity of this phosphine-bound polymer is superior to that of the phosphine bound to cross-linked polystyrene. The polymer reacted very rapidly with azides to generate iminophosphoranes which could then react with aldehydes to generate imines in good yields and high purities.     

Triphenylphosphine oxide supported on non-cross-linked maleimide-styrene copolymer: application as a novel Hendrickson reagent

A new triphenylphosphine oxide reagent linked to a linear maleimide-styrene copolymer is synthesized. This phosphine-bound copolymer is converted to copolymer-supported triphenylphosphine ditriflate as a novel Hendrickson reagent by treatment with triflic anhydride. This reacts rapidly in various dehydration reactions such as anhydride, ester and amide formation. This linear and soluble support is also easily recovered and recycled several times without loss of efficiency.     

Free radical allyl transfers utilizing soluble non-cross-linked polystyrene and carbohydrate scaffold supports

Free radical allylations were studied using (1) soluble non-cross-linked polystyrene supports, (2) carbohydrate scaffolds, and (3) a combination of both synthetic motifs. Allylations on these custom designer supports provide easily purified products, free of tin residues. A D-xylose carbohydrate scaffold bearing a bromoester was used for a diastereoselective allyl tin transfer thermally at 80 degrees C and with Lewis acids. This is the first example of a diastereoselective radical reaction directed by a removable polymer-supported carbohydrate auxiliary.     

Direct radical polymerization of 4-styryldiphenylphosphine: preparation of cross-linked and non-cross-linked triphenylphosphine-containing polystyrene polymers

We report herein a simple synthesis of 4-styryldiphenylphosphine and the radical copolymerization of it with styrene, both with and without a cross-linker, to directly form cross-linked and non-cross-linked polystyrene supported triphenylphosphine in which the level of phosphine incorporation can be easily and accurately controlled. The utility of these polymers is demonstrated by their use in Mitsunobu and alcohol bromination reactions.     

Synthesis and evaluation of a new non-cross-linked polystyrene supported hydantoin chiral auxiliary for asymmetric aldol reactions

A new non-cross-linked polystyrene supported chiral hydantoin was prepared and it was shown to be a particularly effective chiral auxiliary for asymmetric aldol reactions, affording high yields and excellent diastereoselectivity. Furthermore, the recovery and recycling of the polymer-supported chiral auxiliary have been successfully achieved without an appreciable reduction in the yield or diastereoselectivity.     

An outer-sphere two-electron platinum reagent

A strategy for designing cooperative outer-sphere two-electron platinum reagents is demonstrated. The novel platinum(II) complex, [Pt(tpy)(pip2NCN)][BF4] (1(BF4-)) (tpy = 2,2':6',2' '-terpyridine, pip2NCN- = 2,6-(CH2N(CH2)5)2-C6H3-), in which the metal is bonded to two pincer type ligands, has been prepared. Treatment of 1 with protic acid results in protonation of the pendant piperdyl groups, allowing for the isolation of [Pt(tpy)(pip2NCNH2)][PF6]3 (2(PF6-)3). 1H NMR spectra of 1 and 2 establish that in each complex the terpyridyl ligand is tridentate, whereas the piperdyl ligand is monodentate, bonded to platinum through the phenyl ring. The structure of the protonated complex was confirmed by an X-ray crystallographic study of crystals of 2(Cl-)3.4H2O. The cyclic voltammagram of 1 exhibits two reversible one-electron reduction waves at E degrees ' = -0.98 V and E degrees ' = -1.50 V (E degrees ' = (Epc + Epa)/2), with a DeltaEp of 65 and 61 mV, respectively. In contrast to other Pt(II) complexes, including 2, this complex also undergoes a nearly reversible two-electron oxidation process at E degrees ' = 0.40 V (DeltaEp = 43 mV, 0.01 V/s). The accumulated data are consistent with the unusual ligand architecture of 1 being capable of stabilizing and allowing for facile interconversion between the Pt(II) and Pt(IV) oxidation states.     

Synthesis of well-defined soluble polystyrene supports: Impact of polymer chain on grafted organotin reagent activity

The synthesis of well-defined soluble polystyrene supports bearing tin hydride functionalities has been achieved in two steps. First, a precursor was prepared by copolymerization of styrene and acetoxystyrene using atom transfer radical polymerization. Prior any modification, this precursor was fully characterized to check its structure. Then in a second part, tin hydride functions were introduced by a four step process. The chemical modification was monitored by IR and ¹H NMR spectroscopies. The soluble support was also characterized by triple detection size exclusion chromatography at each step. Two families of supports were synthesized by varying the molecular weight and the degree of functionalization. The effectiveness of these tin hydride supports was tested through the reduction of 6-bromohexene and compared with the small counterpart Bu₃SnH. Measurements of rate constant for hydrogen transfer were also reported.     

Functionalized polystyrene as a versatile support for olefin polymerization catalysts

Heterogeneous polyolefin catalysts based on metallocenium salts of weakly coordinating anions can be prepared via a series of simple reactions from lightly crosslinked chloromethylated polystyrene beads. Catalytic sites are distributed homogeneously throughout the polystyrene particles. The nonporous nature of these catalysts affords a high degree of control over the olefin uptake rate, avoiding problems of premature catalyst fragmentation that often plague high‐surface‐area heterogeneous catalysts based on highly reactive species. The choice of amine as the means of binding or templating allows catalysts based on a wide variety of metallocenes to be readily prepared by the same synthetic approach. The dative interactions between the metallocene cation and the amine functionality of the support material are sufficient to prevent extraction under polymerization conditions to yield excellent particle morphology of the polyolefin product, but they are not so strong as to affect the nature of the polyolefin produced. The polymer‐supported catalysts have been used effectively for the polymerization of ethylene and polypropylene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2979–2992, 2000     

An expedient preparation of Stryker's reagent

A convenient and efficient preparation of Stryker's reagent, [Ph₃PCuH]₆, under homogeneous conditions using silanes as the reducing agent is detailed. The reaction time can be reduced to 1-2 h, and high yields of Stryker's reagent can be routinely achieved. The same method has been extended to the synthesis of [Ph₃PCuD]₆ using Ph₂SiD₂.     

Ethylene polymerization using crosslinked polystyrene as support for zirconocene dichloride/methylaluminoxane

In this paper we report on a zirconocene dichloride/methylaluminoxane catalyst system supported on a crosslinked polystyrene in order to provide ethylene polymerization catalysts for gas phase or slurry processes. Our novel approach uses the Diels‐Alder reaction of cyclopentadiene functions as the final, cross‐linking synthetic step. This provides polymer supported zirconocene catalysts with a homogeneous distribution of active sites. The catalysts were shown to be highly active and to form spherical beads as proven by scanning electron microscopy.     

An enantioselective NMR shift reagent for cationic aromatics

[structure: see text] The water-soluble tetra l-prolinylmethyl derivative of a tetrasulfonated calix[4]resorcarene is an effective chiral NMR solvating agent for compounds with bicyclic aromatic or indole rings. Complexation of bicyclic substrates with the calix[4]resorcarene is likely promoted by hydrophobic effects. The bicyclic substrates have larger association constants with the calix[4]resorcarene than similar phenyl-containing compounds. Substantial enantiomeric discrimination is observed for several resonances in the (1)H NMR spectra of these substrates.     

A soluble polyethyleneglycol-anchored phosphine as a highly active, reusable ligand for Pd-catalyzed couplings of aryl chlorides: comparison with cross and non-cross-linked polystyrene and silica supports

The so-called SPhos phosphine, an extremely active ligand in the amination and Suzuki coupling of sterically-hindered aryl chlorides, has been anchored on different supports such as non-soluble (cross-linked polystyrene) and soluble (non-cross-linked polystyrene and polyethyleneglycol) polymers, as well as high surface silica. SPhos anchored on polyethyleneglycol (PEG-SPhos) showed the best activity for both amination and Suzuki couplings. The PEG-SPhos ligand can be quantitatively recovered from the reaction mixture through precipitation with diethyl ether and recycled in four consecutive runs without loosing activity. ³¹P NMR spectra of the reused anchored ligand showed that deactivation of the PEG-SPhos ligand comes from the progressive oxidation of the phosphine-to-phosphine oxide.     

Highly-loaded amphiphilic polyimino resin: quench reagent and solid support for peptide synthesis

We demonstrate herein that polyimino resin 4a prepared by condensation of α,α′-dichloro-p-xylene, ethylenediamine and tris-(2-aminoethyl)-amine can be successfully exploited as a quench reagent for acids and electrophiles both in aqueous and organic solutions. Scope and limitations of such a resin as a solid support for peptide synthesis were also investigated.     

Vilsmeier-Haack reagent: An efficient reagent for the transformation of substituted 1,3-naphthoxazines into xanthene-type dyes

Derivatives of 1,3-naphthoxazines containing from five to seven-membered spiro ring – under Vilsmeier–Haack reaction conditions are rearranged into novel xanthene-type compounds. All synthesized aminochromene derivatives fluoresce in organic solvents with extra large Stokes shifts (100–133?nm). It was found that compounds containing five-membered annulated aliphatic rings in methanol solution have the best spectral characteristics. These compounds have moderate quantum yields of 28.36–28.94%, and extra large Stokes shifts 106 and 115?nm.     

Preparation of two kinds of chloromethylated polystyrene particle using 1,4-bis (chloromethoxy) butane as chloromethylation reagent

By adopting “grafting from” manner, polystyrene was grafted onto the surface of silica gel particles with an average size of 125 μm in a solution polymerization system, and grafted particle PSt/SiO₂ was prepared. Using 1,4-bis (chloromethoxy) butane (BCMB, it is nontoxic.) as chloromethylation reagent, chloromethylation reaction for the grafted particle PSt/SiO₂ was performed in the presence of Lewis acid catalyst SnCl₄. At the same time, cross-linked styrene-divinylbenzene copolymer (CPS) microsphere also was chloromethylated with the same reagent as PSt/SiO₂, so that two kinds of chloromethylated polystyrene particles were obtained, and they are chloromethylated grafted particle (CMPS/SiO₂) and chloromethylated cross-linked polystyrene (CMCPS) microsphere, respectively. The chemical structures and compositions of the two particles were characterized using Fourier transform infrared and Volhard method. The effects of various factors on the chloromethylation reactions were mainly investigated. The experimental results show that the process to prepare the two kinds of chloromethylated polystyrene particles not only has the character of environment friendness and low cost but also is convenient to control via adjusting various reaction conditions. The main reaction conditions affecting the chloromethylation reactions are reaction time, the added amount of BCMB, and the used amount of solvent and catalyst. They influence the reaction in two respects: (1) the chloromethylation degrees of polystyrene are different under different conditions; (2) Friedel–Crafts cross-linking reaction between polystyrene macromolecules is accelerated or inhibited under different conditions (for CPS microsphere, this cross-linking reaction also is called the additional cross-linking). Under suitable conditions, the two kinds of chloromethylated polystyrene particles with a high chlorine content (about 17%, this chlorine content was calculated based on polystyrene weight) can be gained using SnCl₄ as catalyst and CH₂Cl₂ as solvent at room temperature for 10 h and basically without cross-linking or additional cross-linking.