Substituted salicylaldehyde

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 simultaneous observation of the two EPR spectra has been reported in particular for several tris(dithiocarbamato)iron(III) complexes [Fe(R2NC(S)S)3] where R = cyclohexyl [143], hydroxyethyl [144], and n-butyl [145, 146]. In addition, a considerable number of iron(III) complexes of the type [Fe" -N402] has been found which show EPR spectra of both the HS and LS isomers. These comprise [Fe(X-SalEen)2] Y2 where X-SalEen is the Schiff-base ligand obtained by condensation of X-substituted salicylaldehyde and IV-ethylethylenediamine [147] and similar compounds [100, 148, 149, 150, 151]. For the cobalt(II) complex [Co(terpy)2] (004)2, it is not completely clear whether the two observed EPR spectra are due to HS and LS states related by a spin-state transformation [152]. 

The spiroindolinobenzopyran 2 is a classical example of spiropyran and is easily prepared by the condensation of l,3,3-trimethyl-2-methyleneindo-line (Fischer s base) and salicylaldehyde in anhydrous ethanol or benzene (Scheme 2).ia The nucleophilic attack of Fischer s base on the carbonyl group (like an enamine) gives an aldol product, which undergoes ring closure followed by dehydration. This condensation is reversible therefore, an exchange of the salicylaldehyde component of spiropyran with a different salicylaldehyde is possible. For example, when a solution of spiropyran 2 (Scheme 2) was refluxed with 3,5-dinitro-substituted salicylaldehyde, the open form of 6,8-dinitro-BIPS was obtained.2... 

The Fe(III) complexes of R-substituted salicylaldehyde thiosemicarbazone (R-thsa2- Fig. 6) are among the most studied spin crossover materials of this family. The crystal structures of several of them have been determined at various temperatures. The iron-donor atom distances are compiled in Table 2. The Fe(III) ion is in a distorted FeS2N202 octahedron formed by two thiosemicarbazone ligands, which are geometrically arranged in such a way that the S and O atoms are located in cis positions, whereas the N atoms occupy trans positions, i.e. each tridentate molecule coordinates in an equatorial plane [101]. 

In the following, various Fe(III) compounds of R-substituted salicylaldehyde thiosemicarbazones will be discussed according to the criteria mentioned above, although it should be pointed out that a comparison of these materials may be rendered less meaningful due to the possible occurrence of different polymorphs. Moreover, upon variation of one substitution parameter, several other structural features may also be changed simultaneously. For instance, a change in outer-sphere cation or the introduction of a substituent at the salicylaldehyde moiety is frequently associated with increased hydration of the Fe(III) material. 

The various tautomers and rotamers of alloxan have been examined in detail by the MNDO method and it is predicted that the keto form is most important in the gas phase, although in solution the monohydroxy forms are also thought to contribute. A mass spectral study has been used to investigate the enol-keto tautomeric equilibria of a series of substituted salicylaldehyde and 2-hydroxynaphthaldehyde Schiff bases. In neutral, ethanolic solutions, the cis- and trans-tm forms of 4,5-dimethyl-2-(2 -hydroxyphenyl)imidazoles (393) and (394) have been found to exist in equilibrium in the ground state. However, in neutral aqueous solutions, the trans-eao and keto forms (394) and (395) were the only species detected. Deuterium isotope effects on... 

The new series of oxovanadium(iv) complexes with Schiff bases derived from 2-aminothiophenol and substituted salicylaldehyde (40) or 2-hydroxy-naphthaldehyde has been synthesized and characterized. The ligands (40a),... 

I2 vapor is extremely corrosive while scandium compounds are moisture-sensitive and very expensive. In addition, these reactions are carried out in an environmentally unfriendly solvent, CH2CI2. We have reported the bismuth triflate-catalyzed synthesis of substituted dihydro-2//-1-benzopyrans by the condensation of substituted salicylaldehydes with 2,2-dimethoxypropane (Scheme 3) [22]. 

Similar in style to the above are the base-catalyzed intramolecular cyclizations of diesters (116) and substituted salicylaldehydes (117), Dieckmann and Perkin condensations, respectively (36JCS212, 36JCS419, 40JCS787). 

A series of stable 2-aminobenzopyrylium salts has been prepared by the reaction of substituted salicylaldehydes with nitriles in an aprotic polar solvent (81ZC408). 

The most studied bidentate Schiff bases containing an N,0 donor set are those derived from substituted salicylaldehyde derivatives, since they have been widely used as ligands for many transition metal complexes.73 They have also been investigated extensively because of their meso-morphism in the solid state. Those which have been structurally characterized are collected in Table 7 together with some structural parameters of interest. 

Carboxy-substituted benzofurans have been prepared under solventless phase-transfer conditions (solid potassium carbonate/tetrabutylammonium bromide) by condensation of a substituted salicylaldehyde with chloroacetic acid esters (Scheme 3.1)2. Similarly, 2-carboxyaryl-substituted benzofurans were prepared by condensation of a set of salicylaldehydes with a-tosyloxyketones in the presence of solid potassium fluoride doped alumina (Scheme 3.1)3. In each case, a domestic microwave instrument was employed. 

By far the most important and widely used metal-complex dyes are derived from azo compounds. Although they deliver a multitude of shades, only a few basic components are necessary to produce metal-complex azo dyes. The most useful starting materials are the amines 1-4, which serve as diazo components for reaction with suitable coupling components to give tridentate azo ligands. In addition, the amines 1 and 2 can be condensed with salicylaldehyde or arylazo-substituted salicylaldehydes to give tridentate azomethine ligands. 

Unsymmetrical 1 2 chromium complexes based on an azo and an azomethine dye ligand can be prepared directly from a mixture of a 1 1 chromium complex and equimolar quantities of an 2-aminophenol, an anthranilic acid, or an aliphatic amino acid, and of salicylicaldehyde or a substituted salicylaldehyde [22],... 

A series of nitrile-containing benzo[fc]furans were synthesized and evaluated as melatonin receptor ligands <02JMC2788>. Substituted l-(bromoacetyl)azulenes reacted with substituted salicylaldehyde to furnish l-(2-benzofurancarbonyl)azulenes, but no yields were recorded <02JHC671>. 

The reaction was also successful for substituted salicylaldehydes. When Jacobsen came to develop his asymmetric epoxidation, which, unlike the Sharpless asymmetric epoxidation, works for simple alkenes and not just for allylic alcohols, he chose salens as his catalysts, partly because they could be made so easily from salicylaldehydes. For example ... 

A BIPS having hydrogen rather than alkyl on the l -nitrogen atom could possibly be formed from the reaction between a 2,3,3-trialkylindolenine and a salicylaldehyde. However, the reactions between 4-nitro-2,3,3,7-tetramethylindole-nine and five different substituted salicylaldehydes (3-methoxy-5-nitro 5-nitro 3-bromo-5-nitro 3-nitro-5-methoxy and 3-nitro) gave only the 2-hydroxy(substitu-ted)styryl dyes, which were not solvatochromic or photochromic. The yields were 3-7% based on 5-nitro-2-methylphenylhydrazine, the precursor of the indolenine used. The NMR, UV, and mass spectrometry (MS) evidence excluded spiro or open zwitterionic structures for these products.81... 

The template synthesis of mixed nitrogen and oxygen donor macrocycles are mainly based on substituted salicylaldehydes or salicyl-aldehyde-metal complexes (82), e.g.,... 

Nitrobenzofurans (21) have been obtained by the condensation of substituted salicylaldehydes with bromonitromethane,18,19 a versatile reagent useful for the synthesis of various other nitro-heterocycles. The yields however, are variable (5-52%) [Eq. (3)]. 

Substituted salicylaldehydes react with hydrazoic acid in sulfuric acid to give indoxazenes 50,51 up to 15% of the corresponding 2-aminobenzoxazole (32) may be obtained as a by-product. The reaction is a variant of the Schmidt reaction, in which the intermediate nitre-nium ion may cyclize at once to the indoxazene, or rearrange and react with more hydrazoic acid, ultimately providing the benzoxazole. 

A great number of Schiff-base complexes of oxovana-dium(IV) have been studied by X-ray diffraction. Many of these bases contain 0,0,N,N-donor atoms in ligands formed from reaction between substituted salicylaldehyde and aliphatic or aromatic amines, " but examples with S-donor ligands have also been reported. The distorted square... 

Similarly, when the substituted salicylaldehydes 5 were reacted with the (Z)-/ -nitrostyrenes 6, a variety of dihydrobenzopyrans rac-1 were obtained diastereomerically pure in 41-80% yield58. Note that the products rac-1, bearing three stereocenters, arise from an additional diastereoselective addition of the intermediate nitronate anion to the aldehyde carbonyl group. Again, the relative configuration of the product(s) is in accord with a thermodynamically controlled reaction. 

The same conversion is successfully catalyzed by using in-situ generated complexes of Ti(OPr )4 and tridentate Schiff bases (Stmcture 54), which are derived from substituted salicylaldehydes with chiral aminoalcohols [85]. Another similar chiral reagent is derived from reaction of titanium tetraisopropoxide and the Schiff base of 3,5-di-tert-butylsalicylaldehyde and (5)-valinol. The mechanism and stereoselectivity of these chiral Lewis acids are discussed by Corey and co-workers. Other chiral Ti Schiff base complexes have been employed in asymmetric TMSCN addition to benzaldehyde [85]. 

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