Salicylaldehyde catalyst

Basic catalysts other than alkali acetates have been employed in the Perkin reaction thus salicylaldehyde condenses with acetic anhydride in the presence of triethylamine to yield coumarin (tlie lactone of the cis form of o-hydroxy-cinnamio acid) together with some of the acetyl derivative of the trans form (o-acetoxycoumaric acid) ... 

Benzofurans have been prepared by microwave-accelerated cyclocondensation of differently substituted salicylaldehydes 182 with esters of chloroacetic acid 183 in the presence of K2CO3 (used as the solid support) and tetrabutyl-ammonium bromide (TBAB) as phase transfer catalyst [120]. This method seemed general regarding the variations at the benzene ring and the nature of the ester moiety (Scheme 66). 

The first asymmetric intramolecular Stetter reactions were reported by Enders and co-workers utilising triazolium salt pre-catalyst 125. Treatment of substrate 123 generated 1,4-dicarbonyl compound 124 in good yield and enantioselectivity [56]. These salicylaldehyde-derived substrates 123 have since become the standard test substrates for the development of new catalysts for the asymmetric intramolecular Stetter reaction. Bach and co-workers have achieved moderate enantioselectivities using axially-chiral thiazolium pre-catalyst 126 [41], whilst Miller and co-workers have developed peptidic thiazolium pre-catalyst 127 [57]. In 2005, Rovis and coworkers showed that the NHCs derived from triazolium salts 128-130 were excellent catalysts for the asymmetric intramolecular Stetter reaction of a wide range of substrates, giving typically excellent yields and enantioselectivities [58]. The iV-pentafluorophenyl catalyst 129 currently represents the state of the art in asymmetric Stetter reactions (Scheme 12.24) [59]. 

This chapter compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It is proposed that with the basic catalyst, Mg/Fe/0, the tme alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacts with phenol to yield salicyl alcohol, which rapidly dehydrogenates to salicyladehyde. The latter was isolated in tests made by feeding directly a formalin/phenol aqueous solution. Salicylaldehyde then transforms to o-cresol, the main product of the basic-catalyzed methylation of phenol, likely by means of an intramolecular H-transfer with formaldehyde. With an acid catalyst, H-mordenite, the main products were anisole and cresols moreover, methanol was transformed to alkylaromatics. 

Figure 44.5. Conversion of phenol ( ), molar selectivity to anisole (X), o-cresol (O), p-cresol (A), 2,6-xylenol (O), salicylaldehyde ( ) and polyalkylated phenols ( ) as functions of temperature. Catalyst H-mordenite. Feed composition N2 89.3%, formaldehyde 1.7%, phenol 0.46%, methanol 0.03% and water 8.5%.

Tests were carried out with the Mg/Fe/0 catalyst, with the formalin/phenol feed and with variation of the residence time, in order to obtain information on the reaction intermediates. Very low residence times (e g., smaller than 0.1 s) and a low temperature (250°C) were used in order to isolate the intermediates, which were supposed to be extremely reactive. Salicylaldehyde was found to be a primary product, since its selectivity extrapolated to nil conversion was higher than zero ... 

Synthesis of complex 1. The pentadentate salen catalyst 1 was synthesized as described (9). In short, the tosylated 2-[2-(2-methoxyethoxy)-ethoxy]-ethanol 2 (10) was reacted with 2,4-dihydroxybenzaldehyde 3 to yield 4-alkoxy salicylaldehyde 4 after chromatographic purification (eq. 1). Subsequent condensation of 4 with 1,3-diaminopropanol yielded water-soluble salen ligand 5 in sufficient purity and 89% yield (11). The formation of an azomethine bond is indicated by a shift of the NMR signal for the carbonyl carbon from 194.4 ppm in aldehyde 4 to 166.4 ppm for the imino carbon in 5. The pentadentate ligand 5 was then treated with copper(ll) acetate in methanol to obtain the dinuclear copper(ll) complex 1 as a green solid (eq. 2) (11). 

Several catalysts that can effect enantioselective epoxidation of unfunctionalized alkenes have been developed, most notably manganese complexes of diimines derived from salicylaldehyde and chiral diamines (salens).62... 

An easy means of access has recently [59] been reported by NH4OAc on silica gel as catalyst for the condensation of salicylaldehyde (and 2-hydroxy-1-naphthylalde-... 

A number of structurally very different copper complexes were employed as catalysts. The copper complex of binaphthol-derived phosphoramidite 32 and the Schiff base complex 53 (derived from salicylaldehyde and phenylglycine) gave promising results in a screening reaction between 52 and MeMgBr, and 53 was chosen as the candidate for optimization. The effect of solvent (THF or Et20),... 

The complexes [Ru(bpy)2L]+ (HL = acetylacetone, trifluoroacetylacetone, hexafluoroacetylace-tone, tropolone or dibenzoylmethane) have been prepared and characterized they act as catalysts for the oxidation of alcohols, 3,5-di-tert-butylcatechol and alkanes in the presence of appropriate co-oxidants." Perchlorate salts of [Os(bpy)2L] in which HL = salicylaldehyde, 2-hydroxyaceto-phenone or 2-hydroxynaphthaldehyde, are formed from reactions of [Os(bpy)2Br2] with HL. The structure of the salicylaldehyde derivative has been determined. Chemical and electrochemical oxidations of [Os(bpy)2L]" yield the corresponding low-spin Os species from which [Os(bpy)2L]+ can be regenerated." " [Ru(bpy)2L]" (HL = salicylic acid) has been prepared and structurally characterized as the tetrahydrate. Absorptions at 590 nm, 400 nm, and 290 nm in the electronic spectrum have been assigned to Ru bpy CT transitions electrochemical oxidations of the complex have been investigated." ... 

The electronic properties of chiral catalysts were examined. Condensation of the optically active 1,2-diphenylethylenediamine with appropriate C5(5 )-substituted terf-butyl salicylaldehyde derivatives followed by complexation with mangane-se(III) center led to the corresponding catalysts 12a-12e. Then three model substrates, 2,2-dimethylchromene, cA-(3-methylstyrene, and cA-2,2-dimethyl-3-hexene, were subjected to enantioselective expoxidation catalyzed by 5-substituted... 

The Pechmann and Knoevenagel reactions have been widely used to synthesise coumarins and developments in both have been reported. Activated phenols react rapidly with ethyl acetoacetate, propenoic acid and propynoic acid under microwave irradiation using cation-exchange resins as catalyst <99SL608>. Similarly, salicylaldehydes are converted into coumarin-3-carboxylic acids when the reaction with malonic acid is catalysed by the montmorillonite KSF <99JOC1033>. In both cases the use of a solid catalyst has environmentally friendly benefits. Methyl 3-(3-coumarinyl)propenoate 44, prepared from dimethyl glutaconate and salicylaldehyde, is a stable electron deficient diene which reacts with enamines to form benzo[c]coumarins. An inverse electron demand Diels-Alder reaction is followed by elimination of a secondary amine and aromatisation (Scheme 26) <99SL477>. 

Condensation of salicylaldehydes with 2-chloro-3-formylbutene and analogs gave 2-methylenechromcnc derivatives.227 The direct reaction of salicylaldehyde with 2-methyl-2-chlorobutane or 2-methylbutene with catalysts to give 2,2,3-trimethylchromene is reported in a patent228 The structure of the products from salicylaldehyde and dipheny-lenes229,230 has been revised, (see Section V,B).231... 

In 1992, Crabtree and co-workers reported the first nickel catalyst effective for silane alcoholysis.161 The complex, [Ni(tss)]2 (tss = salicylaldehyde thiosemicarbazone), bears a ligand that contains O and N donor groups and a semicarbazide sulfur. Alcoholysis of Et3SiH with ethanol or methanol occurs at room temperature in 50% dimethyl sulfoxide-benzene. However, the reaction is inhibited in the presence of strong donor ligands, H2, or atmospheric pressure of CO. 

ALET3-teff-BuTYL Chloride-Cobalt Compound Catalyst. PVC, 20 grams, was suspended in 190 ml chlorobenzene, and the resultant slurry was cooled to 5°C. The addition of 2 grams of butadiene was followed by the successive addition of 0.01 mmole of cobalt (II) bis(salicylaldehyde imine), 2 mmoles of terf-butyl chloride, and 2 mmoles of triethylalumi-num. The reaction mixture was stirred at 8°C for 60 minutes and poured into 1 liter of methanol. The vacuum-dried product weighed 21.9 grams, representing an add-on of 5.1%. 

A kinetic study of the Schiflf base condensation of m-toluidine with salicylaldehyde has examined the effects of proton, hydroxide, general base, and transition metal catalysts, and also solvent effects.25... 

Coumarin is formed from acetic anhydride and salicylaldehyde in the presence of triethylamine as the base catalyst. It is the lactone of the (Z)-form of o-hydroxycinnamic acid some of the ( )-isomer in the form of its acetyl derivative (o-acetoxycinnamic acid) is also obtained (Expt 6.138). 

Effect of anion, solvent, complexing agents Salts of cuprous ion other than acetate have been tried as catalysts. Cuprous salicylaldehyde is effective in activating hydrogen at about the same rate as is cuprous acetate. Cuprous salicylaldimine, salicylaldehyde-urea, salicylaldehyde-... 

Another example of minimizing the reaction steps necessary for synthesis is the direct conversion of cresols into hydroxybenzaldehydes, replacing the Reimer-Tiemann reaction in which phenol is reacted with chloroform in the presence of KOH. Hydroxybenzaldehydes are used in pharmaceuticals, perfumes, and colors. In the direct oxidation cresols are reacted with oxygen in the presence of Cu/Co/C catalysts forming the salicylaldehyde [49]. 

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