Reduction aromatic aldehydes

Like any aldehydes aromatic aldehydes undergo Clemmensen reduction [758, 778] and Wolff-Kizhner reduction [759, 774] and give the corresponding methyl compounds, generally in good yields. The same effect is accomplished by conversion of the aldehydes to p-toluenesulfonyl hydrazones followed by reduction with lithium aluminum hydride (p. 106). 

The full paper has appeared on a synthesis of steviol. The route was based on the stereocontrolled photoaddition of allene to the cyclopentene-1-aldehyde (178), reduction of the aldehyde, and then solvolysis of the methanesulphonate (179). Papers on the synthesis of the aromatic ether (180) and on the construction of the c/d ring system of the alkaloid chasmanine " have been published. 

Lysine, 4-amino Aldehydes (aliphatic, aromatic, Reductive alkylation... 

Bis(N-inethylpiperazinyl)aluniinum hydride (li. This hydride was originally prepared from aluminum hydride and N-methylpiperazine, and was used to reduce carboxylic acids directly to aldehydes. It can be prepared more conveniently from lithium aluminum hydride and the amine. It is useful for reduction of aliphatic and aromatic acids to aldehydes (80-95% yield). Significantly, it reduces a,p-unsaturated acids to aldehydes without reduction of the double bond (70-80% yield). ... 

Reductions. Aldehydes, aromatic acids and their esters are reduced by PMHS in the presence of Bu NF. Aluminum chloride is also an effective catalyst in the selective reductive cleavage of 2-phenyl-1,3-dioxanes and dioxolanes (e.g., 4-O-benzyl derivatives from the 4,6-benzylidene sugars).- ... 

On the other hand, use of acetic acid as the solvent, or addition of a few drops of concentrated HCl or HCIO4, facilitates formation of the hydrocarbon. Platinum oxide is rapidly deactivated by aromatic aldehydes through reduction of the catalyst to a lower oxidation state. This difficulty is circumvented by reactivation after shaking the reaction mixture with air or by various additives such as Fe ... 

Reductive couplings. Aliphatic and aromatic aldehydes undergo reductive dimerization on exposure to TiBr2-Cu. 

Pinacolization. In dichloromethane, aromatic aldehydes undergo reductive dimerization under the influence of TiClj. The reaction is highly stereoselective, giving the iy/j-l,2-diols predominantly syn anti 200 1). A cross-coupling is the major reaction when methyl phenylglyoxylate and pyridine are present, and p-amino-a-hydroxy esters are obtained with the further introduction of an amine. ... 

Intermolecular aldehyde/alkyne reductive couplings involving PBua and EtaB have been explored on a variety of systems ranging from simple to quite complex [22]. Aromatic alkynes are generally the best substrates, whereas more substrate generahty is observed on the aldehyde component (Scheme 7). In the course of examining asymmetric couplings (see Sect. 2.2.4), a variety of different monodentate phosphines were examined [23]. 

Coordinated dienes containing CHO groups have properties of aromatic aldehydes therefore, they differ from a,]8-unsaturated aldehydes. The reduction by means of Na[BH4] leads to a primary alcohol, and the reaction with MeMgl gives a secondary alcohol [equation (8.62)]. 

A related direction concerns the elaboration of coupled systems, where one substrate is oxidized into an added-value product, while another one is reduced, also giving a product with added value. As an example, coupled systems for selective oxidation of aromatic alcohols to aldehydes and reduction of nitrobenzene into anihne can be mentioned. This oxidation-reduction couphng was realized using a cadmium-based composite material as a photocatalyst under visible-hght illumination, giving, in one-pot, 45% and 26% yields of benzaldehyde and anihne, respectively. 

Dai X, Xie M, Meng S, Fu X, Chen S. Coupled systems for selective oxidation of aromatic alcohols to aldehydes and reduction of nitrobenzene into aniline using CdS/g-C3N4 photocatalyst under visible light irradiation. Appl Catal B Environ. 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

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