Polystyrene supported catalysts, synthesis

The multifaceted applications of phase-transfer catalysts (PTC) in organic synthesis contributed decisively to the establishment of organic catalysts as useful preparative tools. Polymer-supported PTC was examined extensively but it was noted that the catalytic activity of the insoluble polystyrene-supported catalysts was strongly reduced in com-... 

An intramolecular palladium(o)-catalyzed cross-coupling of an aryl iodide with a trans vinylstannane is the penultimate maneuver in the Stille-Hegedus total synthesis of (S)-zearalenone (142) (see Scheme 38).59 In the event, exposure of compound 140 to Pd(PPh3)4 catalyst on a 20% cross-linked polystyrene support in refluxing toluene brings about the desired macrocyclization, affording the 14-membered macrolide 141 in 54% yield. Acid-induced hydrolysis of the two methoxyethoxymethyl (MEM) ethers completes the total synthesis of 142. 

In a more recent study, Wang and coworkers have discussed microwave-assisted Suzuki couplings employing a reusable polymer-supported palladium complex [141]. The supported catalyst was prepared from commercial Merrifield polystyrene resin under ultrasound Bonification. In a typical procedure for biaryl synthesis, 1 mmol of the requisite aryl bromide together with 1.1 equivalents of the phenyl-boronic acid, 2.5 equivalents of potassium carbonate, and 10 mg of the polystyrene-... 

There has been considerable recent research interest in the activation of carbon monoxide en route to more complex organic molecules. Among the various reactions that have been investigated and/or newly discovered, the transition metal catalyzed reduction of CO to hydrocarbons (Fischer-Tropsch synthesis) has enjoyed particular attention (l- ). Whereas most of the successful efforts in this area have been directed toward the development of heterogeneous catalysts, there are relatively few homogeneous systems. Among these, two are based on clusters (10,11) and others are stoichiometric in metal (12-17). In this report we detail the synthesis and catalytic chemistry of polystyrene ( ) supported... 

Soluble polymers that have been used in hquid-phase methodologies are listed in Fig. 5.1 [3, 7, 8, 34, 35]. Polyethylene glycol and non-cross-linked polystyrene are some of the most often used polymeric carriers for organic synthesis and have found frequent use in the preparation of soluble polymer-supported catalysts and reagents consequently, a brief discussion of these polymers is warranted. 

The synthesis of the polystyrene-supported biguanides was performed in the same way as for the soluble ones. The starting polymers were gel-type polystyrenes with chloromethyl or 6-bromohexyl groups prepared according to Merrifield or Tundo respectively.19. These new catalysts were obtained either by sequential syntheses on aminated polystyrene or by covalent grafting of ready made biguanides. 

Progress in process development for the synthesis of 2 recently was made by Behr and co-workers. Extraction of a palladium-phosphine catalyst by use of 1,2,4-butanetriol as extractant offers an effective separation from 2 and also an easy catalyst recycling [14]. Fitter et al. have shown that immobilization of homogeneous palladium catalysts on a polystyrene support is an alternative to the homogeneously catalyzed synthesis which enables easy catalyst recovery [15]. 

It is instructive to compare these new supported sulfonic acids with the well established polystyrene-supported sulfonic acids which have been used as acid catalysts in reactions such as MTBE synthesis for many years. These sulfonated polymers are generally thought to be limited in application because of their relatively low acid strength and poor stability at reaction temperatures above 150 However, we and others have... 

Laibinis used a three steps synthesis for the polystyrene-supported salen 307 (Scheme 126) [189-190], Asymmetric epoxidation was carried out in biphasic conditions with NaOCl as the oxidant in presence of 307mii as catalyst. The enantiomeric excesses and the yields of AE with styrene (9% ee, 7% yield), cA-P-methylstyrene (79% ee, 2% yield) or dihydronaphtalene (42% ee, 46% yield) were low to modest. 

The application of polymer-supported catalysts has now been extended to the synthesis of complexes between transition metal derivatives and structurally ordered macromolecular ligands to give catalytic systems exhibiting high activity and stereoselectivity. Polystyrene and polymethacrylate resin and polystyrene-divinylbenzene-polystyrene-polybutadiene block copolymers, as well as vinyl-functionalized polysiloxanes grafted onto silica, are very suitable polymers for heterogenization of mostly Pt and Rh complexes. Moreover, polyamides exhibit much higher thermal stability than conventional polystyrene supports (114). 

Dendrimer- and polymer-supported catalysts can be employed in the ATH of sultam precursors [71, 72], including examples where the supporting material has sulfonyl groups and therefore assists reactions in water [73]. The synthesis of an amphiphilic polystyrene-type immobilized TsDPEN ligand and its application in ATH of cyclic sulfonimines has been reported (Fig. 16) [74]. 

Rahmatpour A (2012) Polystyrene-supported AICI3 as a highly active and reusable heterogeneous Lewis acid catalyst for the one-pot synthesis of quinoxalines. Heteroatom Chem 23(5) 472-477. doi 10.1002/hc... 

Another reaction in water via intramolecular Ullmann type C-N coupling reaction has been developed by Huang et al. [78]. The catalyst in this case is a recyclable, environmentally benign heterogeneous CuI/PSP (polystyrene-supported pyrrole-2-carbohydrazide) utilized for the synthesis of imidazo[l,2-a]quinoxaline (Scheme 54). 

Dygl996 Dygutsch, D.P. and Eilbracht, P, Synthesis of Cyclopen-tanone Derivatives with Polystyrene-Supported Cyclopentadi-enyl Rhodium Catalysts, Tetrahedron, 52 (1996) 5461-5468. 

Nguyl995 Nguyen, S.T. and Grubbs, R.H., The Synthesis and activities of Polystyrene-Supported Olefin Metathesis Catalysts based on Cl2(PR3)2Ru=CH-CH=CPh2, J. Organomet. Chem., 497 (1995) 195-200. 

Very recently, Gangireddy et al. elaborated the synthetic scope for the 2-aminofluorene-substituted phosphonate derivatives (58) using a variety of aliphatic/alicyclic/aromatic aldehydes via three-component one-pot Kabachnik-Fields reactions under solvent-free microwave irradiation, just replacing the catalyst with polystyrene-supported p-toluenesulfonic acid (PS/PTSA). This procedure is also a simple, high yielding, straightforward, environmentally-friendly method for the synthesis of biologically relevant a-aminophosphonate scaffolds (Scheme 27). ... 

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