Polymer-supported thioanisole: a versatile platform for organic synthesis reagents

A new cross-linked polystyrene-supported thioanisole reagent is reported. This reagent incorporates the flexible JandaJel™ cross-linker and can be treated with methyl trifluoromethanesulfonate to form the corresponding sulfonium salt. This salt can in turn be deprotonated to form a polymer-supported sulfur ylide that is able to react with aldehydes and ketones to form epoxides. The thioanisole reagent can also be oxidized to form an insoluble sulfoxide reagent that is useful in Swern oxidation reactions. In these reactions, the polymer-supported thioanisole-based reagents can be recovered, regenerated and reused.     

可溶性高分子负载催化剂*

均相催化剂的负载化是解决催化剂分离与回收的一条有效途径,也是绿色化学研究的重要内容。可溶性高分子,尤其是树状大分子作为另一类催化剂载体近年来受到了越来越多的关注。通过选择合适的反应介质,可溶性高分子负载催化剂可以在均相条件下催化有机反应,反应结束后通过外加不良溶剂的固/液相分离、温度等调控的液/液相分离以及膜过滤等方法进行催化剂的分离与回收。本文概述了在可溶性高分子负载催化剂研究中取得的新进展,重点介绍了负载手性催化剂在不对称催化反应中的应用。     

Use of polymer-supported phenyltin for the creation of aryl-aryl or aryl-heteroaryl bonds via Stille cross-coupling reactions

An insoluble polymer-supported phenyltin reagent was successfully used in Stille cross-coupling reactions with aryl- and heteroaryl-halides. Cross-coupling products were isolated in good to high yields with very low contamination by tin and palladium residues after removal of the residual supported organotin halide. The regeneration and recyclability of the supported phenyltin reagent were also examined and proved to be possible, but required palladium cleaning of the grafted polymer to be efficient along 4 cycles when Pd(PPh₃)₄ was used as catalyst.     

Polymer-supported palladium perfluorooctanesulfonate [Pd(OPf)2]: A recyclable and ligand-free palladium catalyst for copper-free Sonogashira coupling reaction in water under aerobic conditions

Amberlyst A-21, a kind of well-known and cheap polymeric material, was treated with palladium perfluorooctanesulfonate [Pd(OPf)₂] giving a reagent with a palladium loading of 1.94 (wt%). The polymer-supported fluorous palladium catalyzes the highly efficient Sonogashira coupling reaction in water. The reactions can be performed under copper- and ligand-free conditions in an air atmosphere. The palladium catalyst is easily separated and can be reused several times without a significant loss of catalytic activity.     

Polymer-supported N-heterocyclic carbene-rhodium complex catalyst for the addition of arylboronic acids to aldehydes

A novel polymer-supported N-heterocylic carbene (NHC)-rhodium complex was prepared from chloromethyl polystyrene (CM PS) resin using a simple procedure. This polymer-supported NHC-rhodium complex was used as a catalyst for the addition of arylboronic acids to aldehydes affording arylmethanols in excellent yields.     

PS-SNAP, a practical polymer-supported nitrosation reagent in organic synthesis

PS-SNAP was designed and evaluated as a practical nitrosating polymer-supported reagent for the nitrosation of sec-amines. Nitrosated dialkyl amines, alkyl anilines, and bis-anilines were obtained in good yields and high purities after shaking the corresponding amines in the presence of an excess of the newly described reagent followed by simple filtration and removal of solvents.     

Novel polymer-supported organocatalyst via ion exchange reaction: facile immobilization of chiral imidazolidin-4-one and its application to Diels-Alder reaction

The polymer-supported organocatalyst was prepared by ion exchange reaction of MacMillan iminium catalyst with polymer-supported sulfonic acids. Resulting polymeric organocatalyst was effective for Diels-Alder reaction of 1,3-cyclopentadiene and trans-cinnamaldehyde in CH₃OH/H₂O, affording good enantioselectivity and reusability.     

Polymer-supported ytterbium perfluorooctanesulfonate [Yb(OPf)3]: A recyclable catalyst for organic reactions

Amberlyst A-21, a kind of well-known and cheap polymeric material, was treated with ytterbium perfluorooctanesulfonate [Yb(OPf)₃] giving a reagent with a ytterbium loading of 1.34 (wt%). The polymer-supported fluorous ytterbium catalyses the highly efficient nitration, esterification, Fridel-Crafts acylation, and aldol condensation. The catalyst can be recovered by simple filtration and used again without a significant loss of catalytic activity. The protocol avoids the use of fluorous solvents during the reaction or workup, which are expensive and can leach in small amounts.     

Staudinger/aza-Wittig reactions utilizing a novel linear polymer-supported triphenylphosphine as a modified liquid-phase reagent

A new triphenylphosphine reagent linked to a linear maleimide-styrene copolymer is synthesized and is found to be effective for the formation of a variety of imines via the Staudinger/aza-Wittig reaction. This linear polymer-supported triphenylphosphine has a unique solubility behavior and provides for a simple means of purifying the desired imine from the phosphine oxide by-product. The reactivity of this polymeric reagent is superior to that of the cross-linked polymer-supported phosphine reagent.     

A facile route to a polymer-supported IBX reagent

A three-step preparation of a polymer-supported IBX reagent from poly(p-methylstyrene) is reported. This reagent has been used successfully for the efficient oxidation of a series of alcohols to the corresponding aldehydes.     

Facile nucleophilic fluorination by synergistic effect between polymer-supported ionic liquid catalyst and tert-alcohol reaction media system

A highly efficient method was developed for nucleophilic fluorination using an alkali metal fluoride through the synergistic effect of the polymer-supported ionic liquid (PSIL) as a catalyst and tert-alcohol as an alternative reaction media. This PSIL/tert-alcohol system not only enhances the reactivity of alkali metal fluorides and reduces the formation of by-products but also allows the use of a polymer-supported catalyst protocol. As an example, the nucleophilic fluorinations of the model compound, 2-(3-bromopropoxy)naphthalene, with CsF using only tert-amyl alcohol as solvent (for 2 h reaction time), 0.5 equiv of PS[hmim][BF₄] in CH₃CN (for 12 h reaction time), and 0.5 equiv of PS[hmim][BF₄] in tert-amyl alcohol (which is a PSIL/tert-alcohol system for the synergistic effect; for 2 h reaction time) provided 18, 40, and 84% yield, respectively. The characteristics of the nucleophilic fluorination reactions of some halo- and alkanesulfonyloxyalkane systems to the corresponding fluoroalkanes using various alkali metal fluorides are also reported.     

The application of non-cross-linked polystyrene-supported triphenylarsine in Stille coupling reactions

NCPS-AsPh₃ is a soluble polymer-supported triphenylarsine that performed equally well compared to free triphenylarsine as ligands in the Stille cross-coupling reaction of organic electrophiles and organostannanes, with the advantage that it can be conveniently and efficiently separated from the reaction by precipitation, and recycled for further use. The performance of this non-cross-linked polystyrene-supported arsine was found to be generally superior in Stille coupling reactions over the analogous polymer-supported phosphine, paralleling observations on the free ligands. Palladium-catalyzed modification of the polymer-supported arsine was possible through Pd-Ar/As-Ph exchange. Exploiting the ease of isolation of the polymer-supported reagent, the modified arsine is recycled for reuse in the Stille reaction and has led to a reduction in the yield of undesired scrambling products.     

聚合物支载的硼氢化钠还原剂系统对苯乙酮的不对称还原

聚合物支载硼氢负离子还原剂Na^+[P-COO(BH~3)]^-中的活泼氢原子能用于酮的不对称还原。该试剂中加入带手性碳的羧酸或醇, 反应后生成的还原系统还原苯乙酮。     

Ionic liquid-containing polyethylene supported palladium: a green,highly efficient and stable catalyst for Suzuki reaction

The Suzuki coupling was carried out using a new, efficient and reusable polymer-supported Pd/IL catalyst (PEt@IL/Pd) under aqueous conditions. This catalyst was prepared through coacervation approach followed by treatment with Pd(OAc)₂. The FT-IR, SEM, TGA, TEM, XPS, ICP and EDX techniques were employed to characterize the PEt@IL/Pd. This catalyst exhibited high activity in the Suzuki coupling reaction under green conditions. Moreover, the catalyst could be recycled and reapplied for six times with no appreciable loss in its activity. The leaching test also showed high stability of catalytic Pd species under applied conditions.     

Hypervalent Iodine in Synthesis. 90. A Mild and Efficient Method for the Iodination of Pyrazoles

Abstract

The combined reagent of iodobenzene diacetate (or polymer-supported iodobenzene diacetate) with iodine was used as an effective iodinating agent of pyrazoles to the corresponding 4-iodopyrazole derivatives at room temperature with high yields.     

Asymmetric Mukaiyama aldol reaction of silyl enol ethers with aldehydes using a polymer-supported chiral Lewis acid catalyst

Chiral N-sulfonylated α-amino acid monomer (5) derived from (S)-tryptophan was copolymerized with styrene and divinylbenzene under radical polymerization conditions to give a polymer-supported N-sulfonyl-(S)-tryptophan (6). Treatment of the polymer-supported chiral ligand with 3,5-bis(trifluoromethyl)phenyl boron dichloride afforded a polymeric Lewis acid catalyst (16) effective for asymmetric Mukaiyama aldol reaction of silyl enol ethers and aldehydes. Various aldehydes were allowed to react with silyl enol ethers in the presence of the polymeric chiral Lewis acid to give the corresponding aldol adducts in high yield with high levels of enantioselectivity.     

Homogeneous and supported copper(II) acetate as catalyst for CO coupling reactions

The reactivity of copper(II) acetate as catalyst in a standard CO coupling reaction has been systematically evaluated. Optimization of the reaction conditions resulted in a protocol involving stoichiometric amounts of reagents, a substoichiometric amount of base and 20 mol% catalyst, at 50 °C in 1,2-dichloroethane and under 1 atm O₂. Next, the reactivity of polymer-supported copper(II) acetate was evaluated. Although it is found that, in contrast to previous results obtained in related CN coupling reactions, the polymer-supported catalyst is in this case less efficient than the corresponding homogeneous one, the catalyst turns out to be conveniently recovered from the reaction mixture by simple filtration.     

Oxidation of Alcohols by Hydroperoxides in the Presence of Polymer-Supported Catalysts: Tetrabromooxomolybdate Supported on a Cationic Polymer

The immobilization of Br₄MoO^? in both poly-p-vinyipyridine with a flexible backbone and silica as a rigid polymer support was carried out. The oxidation of alcohols by t-butyl hydroperoxide (t-BuOOH) was then studied in the presence of the polymer-supported complexes obtained. The differences of the reactivity between catalysts supported by organic and inorganic polymers are discussed. The best carrier for Br₄MoO^? as an oxidation catalyst is a silica modified with silane coupling reagent (dimethyloctadecyl-[3-(trimethoxysilyl)propyl] ammonium chloride).     

Olefin epoxidation with tert-butyl hydroperoxide catalyzed by functionalized polymer-supported copper(II) Schiff base complex

Abstract  

A new polymer-supported Cu(II) Schiff base complex has been synthesized and characterized by elemental (including metal) analysis, FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The catalytic performance of this complex was evaluated in the epoxidation of styrene in acetonitrile/N,N-dimethylformamide (9:1) mixture with 70% tert-butyl hydroperoxide as an oxidizing agent under liquid phase reaction conditions for selective synthesis of styrene oxide. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as temperature, reaction time, solvent, oxidant, catalyst amount, and styrene to hydroperoxide molar ratio for the maximum conversion of styrene as well as selectivity of styrene oxide. We have also investigated the epoxidation reaction of various olefins under the optimized reaction conditions. Comparison between catalytic activities of the polymer-supported Cu(II) Schiff base complex and its homogeneous analogue showed that the polymer-supported catalyst was more active. This heterogeneous complex was reused for five times. The selectivity of the heterogeneous catalyst does not change even after five times of reusing.     

Selective hydrogenation of nitrobenzene top-Aminophenol by the polymer-supported palladium-based mono- and bimetallic catalyst

In acidic reaction medium, polymer-supported monometallic palladium catalyst, PVP-PdCl₂ [(PVP=poly(N-vinyl-pyrrolidone)], is used to catalyze the hydrogenation of nitrobenzene top-aminophenol and aniline. The addition of a second transition metal compound or a very small amount of 2-mercaptopyrimidine gives rise to an increase in the selectivity forp-aminophenol.