Polystyrene supports

A commercial polystyrene supported version is available — scavanger resin (for diol substrate). 

A polystyrene supported DEAD version is commercially available. 

A polystyrene supported version of diisopropyiamine is commercially available. 

The adaptation of the Bischler-Napieralski reaction to solid-phase synthesis has been described independently by two different groups. Meutermans reported the transformation of Merrifield resin-bound phenylalanine derivatives 32 to dihydroisoquinolines 33 in the presence of POCI3. The products 34 were liberated from the support using mixtures of HF/p-cresol. In contrast, Kunzer conducted solid-phase Bischler-Napieralski reactions on a 2-hydroxyethyl polystyrene support using the aromatic ring of the substrate 35 as a point of attachment to the resin. The cyclized products 36 were cleaved from the support by reaction with i-butylamine or n-pentylamine to afford 37. 

The Pictet-Spengler reaction has been carried out on various solid support materials " and with microwave irradiation activation.Diverse structural analogues of (-)-Saframycin A have been prepared by carrying out the Pictet-Spengler isoquinoline synthesis on substrates attached to a polystyrene support. Amine 20 was condensed with aldehyde 21 followed by cyclization to give predominantly the cis isomer tetrahydroisoquinoline 22 which was further elaborated to (-)-Saframycin A analogues. 

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. 

Preparation and catalytic activity of H3PM012O40 catalyst molecularly immobilized on polystyrene support... 

Scheme 10.12 1,3-Dipolar cycloadditions of azomethine ylides with polystyrene-supported Fesulphos ligand.

Polystyrene-supported deoxyribonucleoside-3 phosphoramidites (160), or analogous compounds bound to the support via a piperazine... 

Benzyl ethers are amongst the easiest to cleave by Lewis acids (20). Significant clipping of such bonds, with consequent loss of functionality, resulted during attempted HCl-catalyzed hydrolyses of polystyrene-supported oxazoline intermediates (21, 22) and chiral supports (23, 24). 

Pt-catalyzed hydration of various aliphatic and aromatic alkynes under phase transfer conditions in (CH2C1)2/H20 in the presence of Aliquat 336 led to either a Markovnikov product, mixtures of two ketones, or ketones with the carbonyl group positioned away from the bulky side.72 In the absence of the phase transfer reagent, Aliquat 336, hardly any reaction took place. Recently, a hydrophobic, low-loading and alkylated polystyrene-supported sulfonic acid (LL-ALPS-SO3H) has also been developed for the hydration of terminal alkynes in pure water, leading to ketones as the product.73 Under microwave irradiation, the hydration of terminal arylalkynes was reported to proceed in superheated water (200°C) without any catalysts.74... 

DNA (phosphodiester) hydrolysis has also been examined with [Co(cyclen)(OH2)(OH)]2+ as the active species.1239,1246 Significant rate enhancement of linear1247 and supercoiled1248 double-stranded polydeoxyribonucleotide hydrolysis is observed by immobilizing the Co complex on a polystyrene support. Wider exploration of reactions with DNA follow. 

Another example of microwave-assisted PSR chemistry involves the rapid conversion of amides to thioamides by use of a polystyrene-supported Lawesson-type thio-nating reagent. By use of microwave irradiation at 200 °C in sealed vessels (monomode reactor), a range of secondary and tertiary amides was converted within... 

TABLE 3.1. Asymmetric hydroformylation of styrene using polystyrene supported rhodium catalysts based... 

PS-BEMP = polymer-supported 2-ferf-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazophosphorine EDAC = 1 -[3-(dimethylamino)propyl]-3-ethylcarbodiimide PS-PPh3 = polystyrene-supported PPh3 TBTU = 2(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate. 

The conversion of the polystyrene-supported selenyl bromide 289 into the corresponding acid 290 allowed dicyclohexylcarbodiimide (DCC)-mediated coupling with an amidoxime to give the 1,2,4-oxadiazolyl-substituted selenium resin 291 (Scheme 48). Reaction with lithium diisopropylamide (LDA) and allylation gave the a-sub-stituted selenium resin 292, which was then used as an alkene substrate for 1,3-dipolar cycloaddition with nitrile oxides. Cleavage of heterocycles 293 from the resin was executed in an elegant manner via selenoxide syn-elimination from the resin <2005JC0726>. 

Electron spin resonance (ESR) signals, detected from phosphinated polystyrene-supported cationic rhodium catalysts both before and after use (for olefinic and ketonic substrates), have been attributed to the presence of rhodium(II) species (348). The extent of catalysis by such species generally is uncertain, although the activity of one system involving RhCls /phosphinated polystyrene has been attributed to rho-dium(II) (349). Rhodium(II) phosphine complexes have been stabilized by steric effects (350), which could pertain to the polymer alternatively (351), disproportionation of rhodium(I) could lead to rhodium(II) [Eq. (61)]. The accompanying isolated metal atoms in this case offer a potential source of ESR signals as well as the catalysis. 

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