Hydroxybenzaldehyde derivatives

The reaction was also carried out on the laboratory scale by Bayer 182) (use of special electrolytes and collidine as an auxiliary base), Fuso 183> (use of phosphorus compounds as conductive salts) and UOPl84) (use of alcoholates as electrolytes). Under comparable conditions, p-cresol cannot be oxidized to the corresponding p-hydroxy-benzaldehyde derivatives. If the phenolic hydroxyl group is protected, it is also possible to obtain p-hydroxybenzaldehyde derivatives. 

A highly diastereoselective oxetane formation was identified in the PB reaction of dihydropyridone with a m-hydroxybenzaldehyde derivative (Scheme 7.33). The chiral auxiliary, when bound to the aldehyde, offered a binding site to which the reaction partner could attach by two hydrogen bonds. In the hydrogen-bonded complex that was produced, the two enantiotopic faces of the alkene could be differentiated [52]... 

Bis-salicylidene (or bis-salen) derivatives of 1,2-diaminocyclo-hexane are prepared by treatment of the diamine (or its tartrate salt) with an o-hydroxybenzaldehyde derivative and are used for asymmetric manganese-, cobalt- or chromium-catalyzed reactions. The most important ligand of this type is A(A -bis(3,5-di-terf-butylsalicylidene)-diaminocyclohexane (12), the detailed synthesis of which has been published. Another important ligand is the atropoisomeric derivative (13) (eq 21). ... 

It was shown in the laboratory of P.T. Kaye that the reactions of 2-hydroxybenzaldehydes and 2-hydroxy-1-naphthaldehydes with various activated aikenes proceeded with regioseiective cyclization under Baylis-Hillman conditions to afford the corresponding 3-substituted 2H-chromene derivatives in high yields. Previous attempts to prepare 2H-chromenes chemoselectively via the cyclization of 2-hydroxybenzaldehyde-derived Baylis-Hillman products had proven unsuccessful. Complex mixtures containing coumarin and chromene derivatives were obtained. Good results were observed after the careful and systematic study of the various reactants and reaction conditions. 

H. Stark and co-workers prepared novel histamine Hs-receptor antagonists with carbonyl-substituted 4-[(3-phenoxy)propyl]-1/-/-imidazole structures. The Meyer-Schuster rearrangement was used for the synthesis of one of the compounds. The p-hydroxybenzaldehyde derivative was reacted with ethynylmagnesium bromide to afford a secondary propargylic alcohol. Upon hydrolysis with 2N HCI in a refluxing ethanol/acetone mixture, the corresponding p-hydroxy cinnamaldehyde was obtained. 

Work on the alkaloids of Tiliacora racemosa has been summarized. The position of the free phenolic hydroxy function in one of these, tiliacorine (185 R = H), has been settled by conversion of O-acetyltiliacorine (185 R = Ac) into the p-hydroxybenzaldehyde derivative (186) (Scheme 20). it follows that nor-tiliacorinines A and B also have a free phenolic hydroxy-group at the 12 -position. ... 

Nanoparticulate ZnO was used as an efficient catalyst for the synthesis of cou-marins (84) by the reaction of o-hydroxy benzaldehydes (82) and 1,3-dicarbonyl compounds (83) via Knoevenagel condensation under microwaves and thermal conditions (Scheme 9.24) in moderate to excellent yields (Kumar et al. 2011). This protocol differs from the previous methods for the synthesis of coumarins (84) in terms of simplicity and effectiveness. The application of ZnO/MgO in ionic liquid [bmim] [BF4] was carried out successfully for the synthesis of 4//-pyrans (85) and coumarins (88) at ambient temperature via Knoevenagel condensation reaction of aldehydes (8) or 2-hydroxybenzaldehyde derivatives (86) with active methylene compounds (16, 43, 87) (Schemes 9.25 and 9.26) (Valizadeha and Azimib 2011). The method has several advantages in terms of mild reaction conditions, reusability of the catalyst, high yields of the products, and short reaction times. In comparison with methods mentioned in the literature for the synthesis of 4F(-pyrans (85) and coumarins (88), this protocol has better yield and eco-friendly advantages. 

Building on this chemistry, the same authors developed a novel four-component reaction of p-hydroxybenzaldehyde derivatives, benzylamine derivatives, fumaric acid monoethyl ester and isonitriles in water under microwave irradiation to give natural product-like 5,5,6-fused azaspiro tricycle systems 16 as the main products [11]. This transformation can be assmned to proceed through addition of a final aza-Michael step to the previously developed Ugi/Michael domino sequence, and generates six contiguous bonds and fonr stereogenic centres, including one... 

This observation has led to many other cases in which a large red shift is found, and where ESIPT is invoked to explain this. Since absorption and emission wavelengths can be modified by substituents at various places in the ring system, and there is a considerable dependence on the solvent or other environment (protein, membranes), many reporter systems have been designed on the basis of this idea. Salicylic acid and the related ortHo-hydroxybenzaldehyde derivatives have attracted most attention in the literature for fundamental research, but there are a few other groups of ESIPT molecules that have attracted attention as well. 

The most extensively investigated class of molecules is the ortho-hydroxybenzaldehyde derivatives (Figure 1.13). Almost every conceivable technique has been used to probe its properties in the gas phase as well as in a large variety of solvents and solvent mixtures. Starting with the work of Weller, both steady-state and time-resolved fluorescence remain the most commonly used techniques [96]. Femtosecond spectroscopy gives details of proton transfer... 

Reactions of the Aromatic Ring. The aromatic ring of hydroxybenzaldehydes participates in several typical aromatic electrophilic reactions. Ha.logena.tlon, Chlorination and bromination yield mono- and dihalo derivatives, depending on reaction conditions. Bromination of / -hydroxy-benzaldehyde in chloroform yields 65—75% of the product shown (39). 

Hydroxybenzaldehyde has extensive use as an intermediate in the synthesis of a variety of agricultural chemicals. Halogenation of Nhydroxybenzaldehyde, followed by conversion to the oxime, and subsequent dehydration results in the formation of 3,5-dihalo-4-hydroxybenzonitrile (2). Both the dibromo- and dhodo-compounds are commercially important contact herbicides, hromoxynil [1689-84-5] (2) where X = Br, and ioxynil [1689-83-4]( where X = I respectively (74). Several hydrazone derivatives have also been shown to be active herbicides (70). 

Tyramine is derived by using 4-hydroxybenzaldehyde as the starting material. Vanillin and 0-vanillin can also be used in this synthesis to make the tyramine analogs 2-hydroxy-3-methoxy-B-phenylethylamine and 3-methoxy-4-hydroxy-B-phenylethylamine, respectively. Vanillin is less suspicious to purchase and the potency and elfects of the vanillin made drug are about the same as Tyramine. 

Finally, the intramolecular ring opening of unsaturated 5(4//)-oxazolones derived from 2-hydroxybenzaldehyde is noteworthy. Here, the condensation of hippuric acid and 2-hydroxybenzaldehyde under classical conditions gives a 3-(acylamino)coumarin 602 directly without isolation of an intermediate oxazo-... 

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