Amberlyst acetals

Amberlyst-15, acetone, H2O, 20 h, Aldehyde acetals conjugated with... 

Amberlyst-15, acetone, H2O, 20 Aldehyde acetals conjugated with electron-withdrawing groups tend to be slow to hydrolyze. The use of HCl/THF or PPTS/acetone in the following case was slow and caused considerable isomerization. A TBDMS group is stable under these conditions. ... 

Further improvements to this method have been reported by Bagley. The requirement of harsh thermal conditions to facilitate the cyclodehydration can be minimized by simply adding acetic acid or Amberlyst 15. Alternatively, one could use Lewis acids such as ZnBr2 or Yb(OTf>3 in catalytic amounts. 

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

Yuen et al. [24] first demonstrated the nature of the information that can be obtained regarding chemical mapping within a fixed-bed reactor, using the liquid phase esterification of methanol and acetic acid catalyzed within a fixed bed of H+ ion-exchange resin (Amberlyst 15, particle size 600-850-pm) catalyst as the model... 

The effect of the mode of heating was also studied in heterogeneously catalyzed esterification of acetic acid by isopentyl alcohol in the presence of Amberlyst-15 cation exchange resin catalyst [38], Scheme 10.2. 

Addition reactions such as A-alkylation do not occur readily, and trimethylsilylmethylation of 3,4-diphenyl-l,2,5-thiadiazole 8 with trimethylsilylmethyl trifluoromethanesulfonate at 80°C occurred at N-2 < 1999J(P1) 1709>. The electron-rich 3-hydroxy-l,2,5-thiadiazole can be preferentially methylated on N-2 using trimethyl orthoacetate in toluene to afford the 2-methyl-l,2,5-thiadiazol-3-one in 69% yield <2002EJ01763>, although a mixture of 3-hydroxythiadiazole and neat trimethyl orthoacetate showed a 20 80 ratio of N- versus 0-alkylation products by H NMR. Treatment of 3-hydroxy-l,2,5-thiadiazole with /-butyl acetate under acid catalysis (Amberlyst 15) gave almost exclusively the A-alkylated compound <2002BMC2259>. 

Wang et al. investigated the catalytic behavior of cation exchange resin supported lanthanide(III) salts of the general structure (31) (Scheme 4.15), prepared from Dowex, Amberlite, Amberlyst and other resins [99]. It turned out that Am-berlyst XN-1010 and Amberlyst 15 complexed best with lanthanides(III). Thus, among others, electrophilic substitution of indole with hexanal and Mukayiama-type aldol reaction of benzaldehyde with ketene silyl acetal proceeded in excellent yields under catalytic conditions (Scheme 4.16). 

The latter reaction could be repeated ten times without loss of activity of Yb-XN-1010. Similar results were obtained with ytterbium(III) loaded Amberlyst 15W resin in a two-step one-pot procedure first involving the formation of the active dimethyl acetal from a benzaldehyde derivative which was followed by in situ protection of sucrose (Scheme 4.17) [100]. 

Amberlyst 15 DRY, a sulfonic cation exchange resin with a large surface area, was found to catalyze the imino aldol reaction of imines with ketene silyl acetals to provide racemic y9-amino esters in yields up to 99% [104]. 

Coppola GM (1984) Amberlyst-15, a superior acid catalyst for the cleavage of acetal. Synthesis 1021-1023... 

Trace amounts of cyclic acetals are produced from the [2+2] dimer of cyclooctatetraene on ozonolysis in a 2 1 mixture of dichloromethane and methanol followed by stirring with Amberlyst 15 resin (Equation 39) <2003TL9313>. 

Hydrolysis of acetals.1 Amberlyst-15 is an excellent catalyst for hydrolysis of acetals or ketals in aqueous acetone. It is particularly valuable for hydrolysis of acetals of readily epimerizable aldehydes or ketones. 

Potassium nitrosodisulfonate, 258 Trimethylsilyl chlorochromate, 327 By hydrolysis of acetals or thioacetals Amberlyst ion-exchange resin, 152 Methylthiomethyl p-tolyl sulfone, 192 By isomerization of allylic alcohols N-Lithioethylenediamine, 157 By oxidation of aromatic side chains Trimethylsilyl chlorochromate, 327 From oxidative cleavage of alkenes [Bis(salicylidene-7-iminopropyl)-methylamine]cobalt(II)... 

Cs2.5 in water is hardly separable by filtration because of its very fine particle size. Cs2.5/Si02 prepared by the hydrolysis of ethyl orthosilicate in the presence of colloidal Cs2.5 is efficient for the hydrolysis of ethyl acetate, although it is less active than Amberlyst 15 (200). 

The first example of l,4-benzodiazepin-5-one that incorporates an unsubstituted 2,3-carbon-bond was obtained by hydrolyzing the acetal 69 in THF in the presence of Amberlyst-15 resin <2000S265>. Subsequent heating of the product in toluene with azeotropic removal of water gave the HA>cnTo[e][, 4]dixLcpin-5(4H)-ox e 70 (Scheme 31). 

The resulting salts, 3 and 4, can be hydrolyzed to 2-amino-1,3-diols and 2-amino-1,4-diols, respectively, by treatment with acetate ions supported on Amberlyst A 26 (equation II).13... 

A screw-capped vial containing a magnetic stir bar was charged with Yb(III) resin (160 mg), urea (1.50 mmol), aldehyde (0.50 mmol), and (3-dicarbonyl (0.50 mmol) and heated at 120° for 5 min. Yb(III) resin (170 mg) was added and the mixture was heated at 120° for 48 h with gentle stirring. After cooling to 60°, methanol (1 ml) was added. The suspension was stirred for an additional 30 min then the resin was filtered and washed thoroughly with ethyl acetate. Amberlyst 15 (400 mg) and... 

Recently, Corey and coworkers prepared the cinchonidine-derived bifluoride 20 from the corresponding bromide by passage of a methanolic solution through a column of Amberlyst A-26 OH- form, and subsequent neutralization with 2 equiv. of 1 N HF solution and evaporation (the modified method C in Scheme 9.5). The catalytic activity and chiral efficiency of 20 (dried over P205 under vacuum) have been demonstrated by the development of a Mukaiyama-type aldol reaction of ketene silyl acetal 21 with aldehydes under mild conditions, giving mostly syw-P-hydroxy-a-amino esters 22 as the major diastereomer with good to excellent enantiomeric excesses (Table 9.4) [23],... 

Dehydration of alcohols to ethers, acetals, and ketals Deloxan ASP, Amberlyst Selectivity enhancement Gray et al. (1999)... 

First, the carbonyl group is protected as an acetal under acidic conditions. The most common acid-catalysts are PTSA, CSA, PPTS or, as used in this case, acid exchange resins like Amberlyst 15. An advantage of ion exchange resins is that aqueous work-up is not necessary since the insoluble catalyst can be easily removed by filtration and then recycled. 

For a higher accuracy of the isotherm, the activities in the liquid phase instead of the concentrations can be used. If a thermodynamic model for the computation of the solid-phase activities exists, the equilibrium concentration q and qi can also be calculated from the condition of equal activity, as was done for example for the esterification of acetic acid on Amberlyst 15 using the Flory-Huggins activity model for the solid phase and a UNI FAC model for the liquid phase [17]. 

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