Ammonium acetate catalyzed

Wu and co-workers [77] have developed a novel, simple and efficient method for the synthesis of 2,4,5-triaryl-5//-chromeno[4,3-h]pyridines 37 under microwave radiation via a three-component cascade reaction of 2-hydroxyacetophenone, an aromatic aldehyde and ammonium acetate catalyzed by 2-l -methylimidazolium-3-yl-l-ethyl sulfate. When an insufficient amount of (or no) catalyst was used, solely the corresponding chalcone was formed. Nine new bonds and two new rings are generated in a one-pot process with water as the only byproduct (Scheme 26). 

DiphenyIpyrrole-3-carbonitriles 30 were produced by ammonium acetate-catalyzed cyclization of 10 with a substituted phenylacetophenone 29 and conjugated azoalkenes 31 yielded l,2-diaminopyrrolo-3-carbonitriles 32. ... 

Scheme 42.41 Enantioselective sequential four-component Hantzsch reaction of dimedone, aromatic aldehydes, ethyl acetoacetate, and ammonium acetate catalyzed by a chiral phosphoric acid.

These reactions are catalyzed by ammonium acetate, the function of which is to generate protonated imines (322). Under mild reaction conditions, condensation of a- hydroxyamino-oximes with acetone dialkylketals takes place. The procedure can be successfully applied in cases where direct condensation with acetone... 

In 1994, Mansuy and coworkers found that a simple ammonium salt, like ammonium acetate alone, is a very efficient cocatalyst for the metalloporphyrin-catalyzed epoxidation of simple alkenes by hydrogen peroxide ". Bases like sodium carbonate, sodium acetate or tetrabutylammonium hydroxide turned out to promote the porphyrin-catalyzed epoxidation without any other additive. Adducts of hydrogen peroxide (with Na2C03, urea, MesNO, PhsPO), which turned out to be particularly useful for reactions in which the concentration of H2O2 in solution needs to be controlled at a fixed level, have been employed by Johnstone and coworkers. 

There are some methods that are specific to HCHO. For example, the Hantzsch reaction of HCHO, collected with a diffusion scrubber, with ammonium acetate, acetic acid, and acetylacetone to form diacetyldihydrolutidine, which is measured using its fluorescence at 470 nm, has been applied to air measurements (Dasgupta et al., 1988, 1990 Kleindienst et al., 1988a,b Lawson et al., 1990 Khare et al., 1997). Reaction with 1,3-cyclohexanedione and ammonium acetate to form a dihydropyridine derivative that is measured by fluorescence has been used in conjunction with a diffusion scrubber (Fan and Dasgupta, 1994). Enzymatic methods have been used in which formaldehyde dehydrogenase catalyzes the oxidation of HCHO to HCOOH in the presence of -nicotinamide adenine dinucleotide, NAD+, which is reduced to NADH. The latter is measured by fluorescence at 450 nm (Lazrus et al., 1988 Ho and Richards, 1990). 

Amino-l,2,4-triazole was alkylated with 4-nitrobenzyl bromide by simply refluxing the mixture in isopropanol to give SO in excellent yield. The aminotriazole SO was deaminated with NaNOa in aqueous HCI and the nitro group was reduced with ammonium formate catalyzed by 10% Pd/C to deliver 47 in an improved yield over the route shown in Scheme 17. Diazotization of 47, reduction of the diazonium salt with sodium sulphite and Fischer indolization of the resulting hydrazine with 4-( /, /-dimethylamino)butanol dimethyl acetal was performed in a single step to afford rizatriptan (4) in 45% yield. 

A series of tetrasubstituted thiazole derivatives 28 has been prepared via a multi-component tandem protocol <07T10054>. Reaction of bis(aroylmethyl)sulfides 23 with aryl aldehydes and ammonium acetate in 1 2 1 ratio under solvent-free microwave irradiation affords 28 in good yields. This reaction presumably starts with Knoevenagel condensation of sulfide with 2 equiv. of aryl aldehydes to give 24. Michael addition with ammonia and concomitant cyclocondensation lead to 26. Base-catalyzed ring opening of 26 to 27 and ring... 

Figure 9.28 HPLC profile of papain-catalyzed B AEE hydrolysis product. Conditions column, juBondapak CN eluent, 0.05 M ammonium acetate-methanol (85 15) flow rate, 2.0 mL/min detector, 254 nm at ambient temperature (From Chen et al., 1982.)...

Mohammadizadeh and co-workers [138] applied for the synthesis of tetrasub-stituted imidazoles 100, a four-component condensation of benzil, an aldehyde, an amine and ammonium acetate under solvent-free conditions using a domestic microwave oven. The condensation is catalyzed by TFA and the desired compounds 100 are obtained in mere 4 min in good to excellent yields. Both ahphatic and aromatic amines could be successfully used (Scheme 77). 

Pyrazin-2-yl)imidazo[l,2-a]pyrazine (475) was obtained as a by-product (10%) in the ammonium chloride-catalyzed preparation of pyrazine carbaldehyde dimethyl acetal from the aldehyde (474) and trimethyl orthoformate (71TL1441). 

Industrially, terephthalic acid is produced by the cobalt(III) acetate, manganese(III) acetate, or ammonium molybdate-catalyzed air oxidation of />-xylene in acetic acid. Sodium bromide reduces the induction period and increases the rate of conversion to terephthalic acid. p-Xylene is initially oxidized to p-methylbenzyl hydroperoxide, and further oxidation gives p-methylbenzaldehyde and p-methylbenzoic acid ... 

Syntheses with malonodinitrile, including Knoevenagel condensations, have been reviewed extensive-jy3.iio.iii Malonodinitrile is one of the most reactive methylene compounds employed in the Knoevenagel condensation and alkylidene and arylidene malonodinitriles are readily available. In many cases the condensation proceeds satisfactorily without any added catalyst, although it is efficiently catalyzed by weak bases like ammonium acetate and piperidinium acetate or amino acids like -alanine. " Sevend... 

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