Cinchona polymer-bound

Janda, Bolm and Zhang generated soluble polymer-bound catalysts for the asymmetric dihydroxylation by attaching cinchona alkaloid derivatives to polyethylene glycol monomethyl ether (MeO-PEG) [84—87]. Since these polymeric catalysts like (24) are soluble in many common solvents they are often as effective as their small homogenous counterparts. Janda et al. prepared catalyst (24) in which two dihydroquinidine (DHQD) units were linked together by phthalazine and finally were attached to MeO-PEG via one of the bicyclic ring system moieties (Scheme... 

The first example of the use of a polymer-bound cinchona alkaloid in the AD was described in 1990 by Sharpless [48,49], The polymer was readily obtained by radical co-polymerization of 9-(p-chlorobenzoyl)quinidine acrylate with acrylonitrile. First applications in dihydroxylations of frans-stilbene using NMO as co-oxidant yielded products with enantioselectivities in the range of 85 -93 % ee. It is interesting that a repetitive use of the polymer was possible without great loss of reactivity, indicating that the metal was retained in the polymeric array. 

Catalytic asymmetric alkylations of 28 have also been carried out with polymer-bound glycine substrates [43], or in the presence of polymer-supported cinchona alkaloid-derived ammonium salts as immobilized chiral phase-transfer catalysts [44], both of which feature their practical advantages especially for large-scale synthesis. 

Mandoli, A., Pini, D., Fiori, M. and Salvadori, P. Asymmetric dihydroxylation with recoverable cinchona alkaloid derivatives a warning note and an improved, insoluble polymer-bound ligand 5 architecture, Eur. J. Org. Chem., 2005, 1271-1282. 

BQC is derived from quinine, which is a member of the cinchona family of alkaloids. Ammonium salts derived from quinidine, a diastereomer of (1) at the hydroxyl substituent, have been used less frequently in catalysis than BQC. Quini-dinium salts often give rise to products with enantioselectivity opposite to that from (1). Other related compounds, such as those derived from cinchonine and cinchonidine (which lack the methoxy substituent on the quinoline nucleus), have found application in organic synthesis. The cinchona alkaloids, as well as salt derivatives in which the benzyl group bears various substituents, have also been studied. Results from polymer-bound catalysts have not been promising. ... 

To explore the possibility of recycling alkaloid-Os04 complexes, several polymer-bound alkaloid derivatives have been used for heterogeneous catalytic asymmetric dihydroxylations. As chiral ligands, polymerized cinchona alkaloids or copolymers of quinine derivatives with acrylonitrile or styrene were studied [46]. In general, lower select vities and decreased rates were observed. 

In addition to the recyclable solid-supported Cinchona-derived PTC catalysts, described in Section 16.2.1.3, polymer-bound glycine substrates... 

In these cases, the polymer was used as an asymmetric support to induce the formation of optically pure product (cf. Worster et al., 1979). Few reports of the use of polymer-bound asymmetric reagents seem to exist in the literature. In this application, the reagent is used either to promote the asymmetric coupling of two groups or to add a group to a compound in an asymmetric manner. By far the largest number of applications have been those in which the polymer-bound asymmetric centers act as catalysts. Asymmetric catalysts, based on either amino acids or cinchona alkaloids, have been used to catalyze the Michael reaction in an... 

Hodl985 Hodge, P, Khoshdel, E., Waterhouse, J. and Frechet, J.M.J., Michael Additions Catalyzed by Cinchona Alkaloids Bound via Their Vinyl Groups to Preformed Crosslinked Polymers, J. Chem. Soc., Perkin Trans. 1, (1985) 2327-2331. 

Polymer-bound Cinchona alkaloids (53) are catalysts for asymmetric Michael additions of carbanions and thiols to a,j -unsaturated ketones, esters and nitro compounds as shown in Scheme 22. Attachment of the alkaloids to the polymer through the remote vinyl group by copolymerization with acrylonitrile or by addition of a polymeric thiol to the vinyl group was required for catalytic activity and stereoselectivity. " " The enantiomeric excesses attained with the polymeric catalysts (28-51 %) are lower than with the soluble alkaloids (36-63%), but the ease of recovery and reuse of the polymers is usually an advantage. 

Another type of insoluble polymer-bound cinchona alkaloid was tested in the AD of olefins. Salvadori has prepared copolymers 294 by solution or suspension copolymerization of chiral monomers 292 with the two styrenic compound 293 and 294 with different monomer ratio (Scheme 117) [178], Both yield and ee were very high and copolymer 295a proved to be more efficient than 295b and 295c. The better swellability due to the lower crosslinking degree has certainly more influence on the catalytic properties and the... 

Michael additions of C-nudeophiles such as the indanone 1 have been the subject of numerous further studies For example, the reaction between the indanone 1 and methyl vinyl ketone was effected by a solid-phase-bound quinine derivative in 85% yield and with remarkable 87% ee by d Angelo, Cave et al. [5], Co-polymers of cinchona alkaloids with acrylonitrile effected the same transformation Kobaya-shi and Iwai [6a] achieved 92% yield and 42% ee and Oda et al. [6b] achieved almost quantitative yield and up to 65% ee. Similarly, partially resolved 2-(hydroxy-methyl)quinudidine was found to catalyze the reaction between 1 and acrolein and a-isopropyl acrolein with induction of asymmetry, but no enantiomeric excesses were determined [7]. As shown in Scheme 4.4, the indanone 7 could be added to MVK with up to 80% ee under phase-transfer conditions, by use of the Cinchona-derived PT-catalysts 9a and 9b, affording the Michael-product 8 or enf-8, respectively [8]. The adducts 8 or ent-8 were intermediates in the stereoselective Robinson anellation of a cydohexenone ring to the indanone 7 [8],... 

In 2005, Lectka and coworkers also reported a-cMorination of acid halide by using polymer-supported cinchona catalyst via a column-based flush and flow system (Scheme 6.37) [66]. To a column of quinine-bound Wang resin 126 were added 120 and 123, then the eluent (THF) was flowed by flushing to afford the corresponding a-chloroesters 125 up to 94% ee. 

A member of the new ligand class for the asymmetric dihydroxylation is the bis(dihydroquinidine) ether of l,4-dihydroxy-9,10-anthraquinone. Cinchona alkaloid ligands bound to soluble polymer supports" are effective catalysts for asymmetric dihydroxylation. 

In addition, in 2(X)4 Mamoka and co-workers [72] synthesized a recyclable fluorous chiral phase-transfer catalyst which was successfully applied for the catalytic asymmetric alkylation of a glycine-imine derivative followed by extractive recovery of the chiral phase-transfer catalyst using fluorous solvent. Later, in 2010 Itsuno and co-workers [73] published a new type of polymer-supported quarternary ammonium catalysts based on either cinchona alkaloids or Maruoka s-type catalyst bound via ionic bonds to the polymeric sulfonates. 

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