Aldehydes by reduction

In analogy to imidazolides, both triazolides and pyrazolides have been converted into aldehydes by reduction with LiAlH ... 

Scheme 2. Double N-alkylation of a sugar aldehyde by reductive animation.65...

Preparation of a -Urethane Protected a-Amino Aldehyde by Reductive Methods... 

Table 3 Preparation of N -Protected Amino Aldehydes by Reduction of Ester and Amide Derivatives n o...

Scheme 5 Synthesis of an a-Amino Aldehyde by Reduction of an a-Amino Acid Phenyl Ester121 ...

Scheme 9 Solid-Phase Synthesis of an a-Amino or Peptide Aldehyde by Reduction of the Corresponding Weinreb Amide LinkerN...

Based on HRh(CO)2(L)2, the mechanism is initiated by the coordination of an alkene molecule, resulting in a sixfold-coordinated complex (A). The following rearrangement to an alkyl rhodium complex happens before a carbon monoxide is added to the complex in the next step and inserted in the rhodium alkyl bond (B). The oxidative addition of hydrogen (C) and the release of the aldehyde by reductive elimination reform the starting rhodium complex (D). 

G. Benz, K.-D. Gundermann, A. Ingendoh, L. Schwandt, Preparation of Aldehydes by Reduction, in Methoden Org. Chem. (Houben-Weyl) 4th ed., 1952-, Aldehydes (J. Falbe, Ed.), Vol. E3, 418, Georg Thieme Verlag, Stuttgart, 1983. 

J. S. Cha, Recent Developments in the Synthesis of Aldehydes by Reduction of Carboxylic Acids and their Derivatives with Metal Hydrides, Org. Prep. Proced. Int. 1989, 21, 451- 477. 

The hydroxycarbenes can easily explain the tormation of aldehydes by reductive elimination from the metal and of alcohols by further hydrogenation. Olefins would be the result of the cleavage of the carbcnoid with the formation... 

The best way to prepare peptide aldehydes from the corresponding N -protected amino acids is by using a handle based on the Weinreb amide.f This commercial handle allows classical solid-phase elongation of peptides using protected Boc or Fmoc amino adds and, at the end of the synthesis, the peptide aldehyde is formed by reduction and concomitant cleavage from the resin with lithium aluminum hydride. Although the 4-hydro-xybenzoic acid handle also allows the preparation of peptide aldehydes by reduction of the resin-bound phenyl ester with lithium tri-tert-butoxyaluminum hydride, a noixture of the aldehyde and the alcohol is always formed. 

Finally, treatment of amides with phosphorus oxychloride gives Vilsmeier complexes, which are often formulated as A-alkylated imidoyl chlorides (59). Irrespective of their precise nature, it has been found that they can be converted very efficiently to aldehydes by reduction with zinc followed by aqueous work-up (Scheme 17). Although the method has only been used for benzaldehyde and a number of chlorinated and brominated analogs, the yields reported are consistently high (87-97%). ... 

Amidines are apparently rather good substrates for selective one-electron reduction to aldehydes. As early as 1908, Merling obtained good yields of some fairly complex aliphatic aldehydes by reduction of the corresponding A/,N-diphenylamidines using sodium in ethanol. As an example, amidine (60) was converted into aldehyde (61) in 60-70% yield. 

Furfuryl Alcohol.—An alcohol, fnrfuryl alcohol, is also known obtained from the aldehyde by reduction. This reduction is brought about by treatment with alcoholic potassium hydroxide, one molecule of the aldehyde being reduced at the expense of a second molecule which is thereby oxidized to the acid. Thus one molecule of pyromucic acid and one of furfuryl alcohol are obtained from two molecules of furfural. 

Zakharkin, L.L, and Khorlina, I.M., Preparation of aldehydes by reduction of nitriles with diisobutyl-aluminium hydride, Dokl. Akad. Nauk SSSR, Ser. Khim., 116,422,1957 Chem. Abstr, 52, 8040f. 1958. 

Scheme 2 Synthesis of A-Boc-a-amino aldehydes by reduction of their corresponding A,0-dimethylhydroxamates [86].

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