Amberlyst 15 polymer-supported

A more effecdve catalyst for the Hetuy reacdon is a polymer-supported base such as amberlyst A-31. Various fi-nitro alcohols can be obtained v/ith the help of amberlyst v/ith or without solvent fEq, 3,14, A recent report claims that amberlite IRA-430 COH-formi or DOWEX-1 COH-formi is more effecdve for the Henry reacdon than amberlyst A-31/ Poly-... 

A more effective catalyst for the Henry reaction is a polymer-supported base such as amberlyst A-21. Various P-nitro alcohols can he obtained with the help of amberlyst with or without solvent (Eq. 3.14).25 A recent report claims that amberlite IRA-420 (OH-form) or DOWEX-1 (OH-form) is more effective for the Henry reaction than amberlyst A-21.26 Poly-... 

Many borohydrides are highly unstable and have to be used as freshly prepared ethereal solutions. However there are instances where the polymer-supported versions are more stable e. g. an Amberlyst anion exchange resin supported borohydride and cyanoborohydride [61], polyvinylpyridine supported zinc borohydride [62] and the corresponding zirconium borohydride [63]. Such compounds, in their labeled forms, should turn out to be very useful. 

Method E (polymer supported catalyst) The alkene (50 mmol) is added to the activated methylene compound (50 mmol) at 0°C and the mixture is stirred for 10 min. Amberlyst A-27 (8 g) is added and the mixture is stirred for a further 15 min and then allowed to stand at room temperature for 4-25 h. The polymer is removed and washed with Et20 (4 x 40 ml). The combined organic solutions are evaporated and the residue subjected to flash chromatography to yield the Michael adduct (75-95%). 

Method D (using polymer supported catalyst) Amberlyst A-26 (OH form) (5 g) is shaken... 

The polymer-supported hydridoiron tetracarbonyl (33 mmol) is prepared by the addition ofFe(CO)5(6.46g, 33 mmol) to KOH (5.6 g, 0.1 mol) in aqueous EtOH (1 1 v/v, 100 ml) under N2. The mixture is heated with stirring under reflux for 2 h and Amberlyst A-26 resin (24 g) is then added and the mixture is stirred for a further 15 min. The resin is collected, washed with degassed H20 (to neutrality), MeOH and Et20, dried at room temperature under a flow of N2, and used immediately. The haloalkane (11 mmol) in THF (50 ml) is added to the resin and the mixture is stirred under reflux for ca. 4 h. When GLC analysis shows the reaction to be complete, the resin is removed by filtration, and the filtrate evaporated under reduced pressure to give the aliphatic aldehyde. 

A molecular sieves (0.5 g) and polymer-supported perruthenate (0.1 g), prepared by adding KRu04 (10 mg, 1 mmol) to Amberlyst IR-27 resin (1 g), in CH2C12 or MeCN (5 ml) at room temperature until TLC analysis indicates complete consumption of the alcohol (ca. 16 h). The mixture is filtered and the filtrate evaporated to yield the carbonyl compound [e.g. PhCHO, >95% (16 h) PhCH=CHCHO, >95% CH2=CH(CH2)2CHO, 62% n-C7HI5CHO, 54% cyclohexanone, 50%]. The resin can be reused without loss of activity. 

Lewis acid (Yb-(III)-reagent supported on Amberlyst 15) in combination with polymer-supported urea scavenging resins (Amberlyst 15 and Ambersep 900 OH) permits a rapid parallel Biginelli synthesis with a simple and efficient purification strategy [126]. 

Fig. 10. Simultaneous use of polymer-supported reagents, (i) Poly(4-vinylpyridinium)dicliromate, cyclohexane, A. (ii) Perbromide on Amberlyst A-26. (iii) Amberlite IRA-900 (4-chloro-l-methyl-5-(trifluoromethyl)-li/-pyrazol-3-ol).

Dioxolans 146 can be considered as masked carbonyl functionalities, and are cleaved under acidic conditions. In solution, the olefination of a dioxolan-protected ketone would therefore be a two-step transformation consisting of deprotection and olefination. Using polymer-supported adds, e.g., strongly addic Amberlyst resin 147 and polymer-supported phosphonates 135 (Scheme 25), the two-step transformation involving the carbonyl compound 137 as intermediate could be performed simultaneously in one pot (Scheme 27) [113]. The product 136 was isolated by filtration. This procedure would not work as a one-pot sequence in solution because the acidic catalyst would immediately quench the basic phospho-nate resin. 

The Nafion polymers supported on carbon had very high activity based on the weight of active polymer. In general, these supported perfluorinated catalysts were 86-180 times as active as bulk Nafion and 234-488 times more active than Amberlyst 15 (see Table 4). 

Halopropionic acid derivatives are readily accessible from lactic acid via its mesylate. Thus, treatment of 156a with AICI3 affords methyl (i )-2-chloropropionate (162) with 88% ee [59]. Reaction of 156a with KF in formamide produces methyl (R)-2-fluoropropionate (163) (96% ee). The use of formamide as solvent not only increases the reaction rate but also favors Sn2 reaction due to its high polarizability. The ti ji is approximately 30 min, and reaction is complete in 3 h [57]. (R)-2-Fluoropropionic acid is prepared from 163 by transesterification with formic acid. Amberlyst A-26 (F ) can be used as an alternate fluoride source in the conversion of mesyl lactates to chiral a-fluoroesters. This polymer-supported reagent produces clean Sn2 reactions [60]. 

Polymer-supported /eagent. Italian chemists have prepared a supported form of this oxidant by reaction of the Cl" form of an anion exchange resin (Anibcriyst A-26, Amberlyst A-29, Amberlite IRA 400, or Ainberlite 904) in llaO with chromium trioxide to obtain a CrOaH" form of the resin. This polymeric reagent oxidizes primary and secondary alcohols in high yield (usually 85-957o). The chloride form of the resin is regenerated by wash with NaOH and HCI solutions. 

General. Polymer-supported sulfonic acids are reliable catalysts for many acid-mediated reactions. Macroretlcular poly-styrene-based resins such as Amberlyst 15 are preferentially used in organic solvents, whereas Dowex resins work better in aqueous solutions. All resins are insoluble and can be separated from reactions by simple filtration. 

In the presence of polymer-supported (PS) SO3H resins, Abulyl ethers and tetrahydropyranyl ethers of alcohols and phenols are formed. Elimination by-products that are formed during the protection of secondary and tertiary alcohols (eq 2) can be avoided using PS-SO3H. Additionally, selective tetrahydropyran protection of primary and secondary symmetrical diols can be undertaken to yield monoprotected products. In the presence of water, Dowex 50W and Amberlite IR-120 give higher yields of monoethers than Amberlyst 15. 

The polymer supported chromic acid (Amberlyst A-26, HCrO" form is commercially available) and has been used to oxidise primary and secondary alcohol to carbonyl compounds and also oxidizes allylic and benzylic halides to aldehydes and ketones. ... 

Polymer-supported chromic acid (Amberlyst A-26, HCr04 -form) has been used to oxidize primary and secondary alcohols to carbonyl compounds (Cainelli et al., 1976a). The same reagent was used to prepare... 

Polymer-supported Lewis acid catalysts based on metals with high coordination numbers, such as Sc, Yb, and Ln, proved to be highly effective in promoting several organic transformations. Umani-Ronchi and coworkers developed polymer-supported indium (I II) Lewis acid [85]. The polymeric In (III) was easily prepared from Amberlyst-Na [86] and In(OTf)3 (Scheme 19.40). They tested the catalytic properties of the polymer-supported indium Lewis acid in the ring... 

Since many oxidation methods use toxic reagents (such as OSO4 and O3) and corrosive acids (such as H2SO4), or they generate carcinogenic by-products (such as Cr ), alternative reactions have been developed. One method uses a polymer-supported reagent—HCr04"-Amberlyst... 

---