Careful control of the reaction conditions in a modified Duff reaction using anhydrous trifluoroacetic acid as the solvent enables the selective synthesis of either 4-substituted 2-formylphenols (5-substituted salicylaldehydes) or 4-substituted 2,6-diformylphenols in one step starting from commercially available 4-substituted phenols in moderate to good yield.Aromatic aldehydes, being one of the most synthetically versatile functional groups in organic chemistry, are often chosen as the starting point in synthetic sequences, especially since a number of such aldehydes are available commercially. Additionally, many aromatic aldehydes are easily prepared in a few steps from simple aromatic precursors. 2 Of these, mono-and diformylated aromatic phenols have proven to be especially important in the synthesis of macrocyclic compounds due to their difunctional nature; as such, they have been of interest to us. 3 We wish to report here an improved synthesis of monoformylated phenols 1 (salicylaldehydes) and diformylated phenols 2 . The new strategy replaces traditionally tedious multistep procedures with a straightforward one-pot synthesis.2,6-Diformylated phenols have been widely used as precursors to binucleating macrocyclic 4-7 and acyclic 8 ligands for use as model systems in bioinorganic chemistry and for fundamental inorganic chemistry studies. Several synthetic strategies have been developed for the synthesis of 2,6-diformylated phenols; however, the published preparations of diformylated phenols are often low yielding and/or involve multistep syntheses. 9-11 The synthesis 8 of 4-tert -butyl-2,6-diformylphenol (2a) in which the product is obtained from 4-tert -butylphenol in four steps (bis-hydroxymethylation of the phenol under basic conditions, selective tosylation of the phenolic hydroxy group, oxidation of the two hydroxymethyl groups to formyl groups using Na 2 Cr 2 O 7 , followed by hydrolytic cleavage of the tosyl group using concentrated sulfuric acid) in an overall yield of less than 4% is representative of a number of these traditional synthetic strategies.A difficulty with most common formylation reactions is that they involve electrophilic attack on the aromatic ring to introduce a functionality than can be easily converted to a formyl group in a few synthetic steps, or during workup. The Vilsmeier 12 reaction, the Reimer-Tiemann 13 reaction, and traditional Duff 14 reactions are all of this type. Since the introduction of a formyl group on to an aromatic ring significantly reduces its electron density, the introduction of a second formyl group is rarely possible. 15 This effect is well known for Friedel-Crafts acylation reactions where clean monoacylation can normally be expected. 16 In view of the above, we were surprised to find that formylation of 4-tert -butylphenol (3a) employing a modified 17 Duff reaction, and using neat trifluoroacetic acid as the solvent instead of glycerol, produced small amounts of 4-tert -butyl-2,6-diformylphenol (2a) along with the expected 5-tert -butylsalicylaldehyde (...
Dianionic and neutral nickel complexes of substituted TTF dithiolate ligands have been prepared showing roomtemperature conductivity of up to 10-1 S cm-1 for the neutral complexes; the crystal structure of the neutral complex [Ni(C1OH1OS&] is reported.
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