Aldehydes, reaction with hydrazines

Azines, Aldehydes react with hydrazine to yield azines the reaction cannot usually be arrested at the hydrazone stage. This reaction may be illustrated by the preparation of bevzalazine from benzaldehyde ... 

Wolff-Kishner reaction (Section 19.9) The conversion of an aldehyde or ketone into an alkane by reaction with hydrazine and base. 

Most reactions with hydrazine are carried out with aldehydes and ketones in the presence of alkali. The reduction proper is preceded by formation of hydrazones that decompose in alkaline medium at elevated temperatures to nitrogen and compounds in which the carbonyl oxygen has been replaced by two hydrogens. The same results are obtained by alkaline-thermal decomposition of ready-made hydrazones of the carbonyl compounds. Both reactions are referred to as Wolff-Kizhner reduction [280]. 

Mercapto pyrimidines 82 were synthesized from acetoacetanilide, dihydroxybenzaldehyde, and thiourea, which were readily alkylated with benzyl chloride to afford 2-benzylthio derivatives 83 (Scheme 32). 83 when reacted with different amines in acetic acid furnished 2-amino derivatives 84 (R = Ar), whereas upon reaction with hydrazine hydrate 83 afforded 2-hydrazinyl derivative 84 (R = NH2), which with different aldehydes gave hydrazones 85 (R = 2-furyl, 2-thienyl). Arylidene thiazolidinone 86 was obtained from 84 with carbon disulfide, monochloroacetic acid, and aryl aldehydes, while 84 with ethyl acetoacetate and different aromatic aldehydes provided pyrazoles 87 (Scheme 32) (10MI9). Such tetrasubstituted pyrimidines act as cyclin-dependent kinase (CDK2) inhibitors. 

Aldehyde (46) has also been converted into diazole-fused thiophenes. Reaction with hydrazine derivatives gave hydrazones (50), which on treatment with acid were converted to diazoles (51). Unfortunately, the nitrogen substituent was sometimes scrambled, leading to mixtures of (51) and (52). The final sulfur oxidation was uniformly high yielding [28,29] (Scheme 6.13, Table 6.3). 

Compounds such as hydroxylamine and hydrazine are similar to primary amines in that they have an NH2 group. Thus, like primary amines, they react with aldehydes and ketones to form imines—called imine derivatives because the substituent attached to the imine nitrogen is not an R group. The imine derivative obtained from the reaction with hydroxylamine is called an oxime, and the imine derivative obtained from the reaction with hydrazine is called a hydrazone. 

Reactions with Hydrazine. TIPSCl reacts with an excess of anhydrous hydrazine to form triisopropy Isilylhydrazine which can be used to prepare TIPS hydrazones (eq 20). TIPS hydrazones are unusually stable in air but readily form asymmetric azines upon treatment with TBAF and a slight excess of ketone or aldehyde (eq 20).31... 

Hydrazones. Reaction of hydrazine with aldehydes and ketones is not generally useful due to competing azine formation or competing Wolff-Kishner reduction. Exceptions have been documented. Recommended conditions for hydrazone preparation are to reflux equimolar amounts of the carbonyl component and hydrazine in n-butanol. - A more useful method for simple hydrazone synthesis involves reaction of the carbonyl compound with dimethylhydrazine followed by an exchange reaction with hydrazine. For substrates where an azine is formed, the hydrazone can be prepared by refluxing the azine with anhydrous hydrazine. gem-Dibromo compounds have been converted to hydrazones by reaction with hydrazine (eq 6). ... 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

HydraZones and Azines. Depending on reaction conditions, hydrazines react with aldehydes and ketones to give hydrazones (33), azines (34), and diaziddines (35), the latter formerly known as isohydrazones. 

The initial step is the formation of hydrazone 2 by reaction of hydrazine with aldehyde or ketone 1 ... 

A useful variant of the imine-forming reaction just discussed involves the treatment of an aldehyde or ketone with hydrazine, H2NNH2, in the presence of KOH. Called the Wolff-Kishner reaction, the process is a useful and genera method for converting an aldehyde or ketone into an alkane, r2c=o —> R2CH2. 

An excellent synthetic method for asymmetric C—C-bond formation which gives consistently high enantioselectivity has been developed using azaenolates based on chiral hydrazones. (S)-or (/ )-2-(methoxymethyl)-1 -pyrrolidinamine (SAMP or RAMP) are chiral hydrazines, easily prepared from proline, which on reaction with various aldehydes and ketones yield optically active hydrazones. After the asymmetric 1,4-addition to a Michael acceptor, the chiral auxiliary is removed by ozonolysis to restore the ketone or aldehyde functionality. The enolates are normally prepared by deprotonation with lithium diisopropylamide. 

Nearly all (extranuclear) hydrazonoquinoxalines are made by treatment of quinoxaline aldehydes, ketones, or their acetals with hydrazine or substituted hydrazine, but a few are produced by diazo coupling. These reactions are illustrated by the following examples. 

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