Polymeric scavenger reagents

Other representative examples in which polymeric scavenger reagents are used, include L. A. Thompson and J. A. Ellman, Chem. Rev. 1996, 96, 555-600 ... 

Polymeric scavenger reagents in organic synthesis (including synthesis of heterocycles) 01EJO1213. 

Table 10. Removal of fluorenylmethoxycarbonyl (Fmoc) group from relatively hydrophobic substrates and scavenging of the by-product dibenzofulvene (DBF) by different polymeric piperazine reagents...

Quinones also show prohibition for polymerization. Benzoquinone, 2,5-dichlorobenzoquinone, and chloroanil are prohibition reagents for polymerization. Those reagents are radical scavengers. A tiny amount of prohibition reagent is effective for stopping pol5mierization. Quinone produces ether radical by reaction with polymer radical as follows ... 

Under certain condition, however, reactions are still preferably conducted in solution. This is the case e.g., for heterogeneous reactions and for conversions, which deliver complex product mixtures. In the latter case, further conversion of this mixture on the solid support is not desirable. In these instances, the combination of solution chemistry with polymer-assisted conversions can be an advantageous solution. Polymer-assisted synthesis in solution employs the polymer matrix either as a scavenger or for polymeric reagents. In both cases the virtues of solution phase and solid supported chemistry are ideally combined allowing for the preparation of pure products by filtration of the reactive resin. If several reactive polymers are used sequentially, multi-step syntheses can be conducted in a polymer-supported manner in solution as well. As a further advantage, many reactive polymers can be recycled for multiple use. 

A disadvantage of borane and borate systems is that the alkylmetallocene cations are more instable and more sensitive to impurities and water. To overcome this higher sensitivity, a dialkyl species can be build by an in situ reaction with tri-isobutylaluminum (TIBA). TIBA acts as alkylation reagent and as a scavenger and stabilizes the dialkyl species in solution it is used as stock solution for the polymerization experiments (Fig. 12). 

Ni(sacsac)P(nBu3)Cl (sacsac = pentane-2,4-dithionate) was activated by AlEt2Cl to form a catalytically active species for the oligomerization of ethene and propene. This study is noteworthy in that it uses in situ UV-VIS spectroscopy to monitor the course of the polymerization. In this reaction, the aluminum reagent serves both to activate the transition metal and to scavenge any moisture present. 

Similar to anhydride-bearing polymers, the synthesis of a poly(norborn-2-en-5-yl-methanol)-derived system, polymerized by a Gmbbs catalyst after scavenging excess of reagent, was reported by Hanson (Tab. 8.3) [42, 43]. 

Baxendale, I.R., Storer, R.I. and Ley S.V. (2003) Supported reagents and scavengers in multi-step organic synthesis, in Polymeric Materials in Organic Synthesis and Catalysis (ed. M.R. Buchmeiser), VCH, Berlin, pp. 53-136. 

Owing to its powerful Lewis acidity, BF3 is an effective reagent in organic synthesis, for example, promoting the conversion of alcohols and acids to esters, the polymerization of olefins and olefin oxides, and acylations and alkylations (in a manner similar to Friedel-Crafts processes). Mechanistic studies of some reactions of the latter type, such as the ethylation of benzene by QH5F, have shown that the BF3 functions as a scavenger for HF via the formation of HBF4 and thus participates stoichiometrically rather than catalytically. 

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