Wolff-Kishner reduction, of aldehydes and

Wolff - Kishner reduction of aldehydes and ketones. Upon heating the hydrazoiie or semicarbazone of an aldehyde or ketone with potassium hydroxide or with sodium ethoxide solution (sealed tube), the corresponding hydrocarbon is obtained ... 

THE WOLFF-KISHNER REDUCTION OF ALDEHYDE AND KETONE HYDRAZONES... 

Alkylfurans are usually obtained by ring synthesis, decarboxylation of alkylfurancarboxy-lic acids, Wolff-Kishner reduction of aldehydes or ketones, or by reduction of halomethyl groups with zinc and acetic acid or LAH (79JOC3420) alkylation is of limited value. The chemistry of these compounds is conventional but oxidation to furancarboxylic acids cannot usually be carried out due to the lability of the ring. NBS bromination (Section 3.11.2.2.5) is a useful route to side-chain substituted compounds but reduction of esters to hydroxymethyl groups and subsequent transformation is often preferable. The haloalkyl compounds are extremely sensitive to resinification but if adequate precautions are taken they are... 

Carbonyl deductions. The classical Wolff-Kishner reduction of ketones (qv) and aldehydes (qv) involves the intermediate formation of a hydrazone, which is then decomposed at high temperatures under basic conditions to give the methylene group, although sometimes alcohols may form (40). 

An important reduction reaction is Wolff-Kishner reduction of carbonyl group on aldehydes and ketones to form hydrazone ... 

Ganter has developed three different approaches to tricyclo[5.2.1.0 ]decane (403), yet another of the nineteen isomeric hydrocarbons of adamantaneland As seen in Scheme XXXIII, the routes involve intramolecular cyclization of keto tosylate 399 followed by Wolff-Kishner reduction of the resulting ketone, thermo-cyclization of 400 and subsequent dechlorination, hydrogenation, and photocycli-zation of aldehydes 401. Majerski s approach involved hypoiodite cleavage of alcohol 402... 

In a more general approach, eight examples of the Wolff—Kishner reduction of aromatic aldehydes and ketones are described using 80% hydrazine hydrate in toluene64 (Scheme 4.37). The reaction times are longer than described in the previous paper because less reactive substrates were used. Still, both the formation of the hydrazone and the reduction step are considerably faster than under thermal conditions the reduction proceeds at ambient pressure and in the absence of a solvent. The microwave reduction is compatible with other reducible functional groups such as aromatic OMe, Me, Cl or COOMe, which can otherwise cause problems under conventional reaction conditions64. 

You can now clearly see the similarity with our target molecule , grandisol, but there are several more steps to carry out yet. The nitrile needs to be got rid of completely—we showed you a few ways of getting rid of functional groups in the last chapter, and the one used here was the Wolff-Kishner reduction of an aldehyde. The aldehyde comes from reduction of the nitrile with DIBAL. 

Dimethoxy-9-methylphenanthrene has been synthesized for this purpose by the Wolff-Kishner reduction of the 9-aldehyde obtained from the 9-carboxylic acid [61], and 3 4 9-trimethoxyphenanthrene has been synthesized via the 9-hydroxycompound by the Bucherer reaction on 3 4-dimethoxy-9-aminophenanthrene [62], It is of interest to note that, contrary to expectations based on [xlv], Holmes and Lee [63] were unable to detect any properties of hydroxycodeine consistent with a carbinolamine structure. 

Hydrox5rprotoemetine (73, R = CHO), an aldehyde of biogenetic interest, has been synthesized for the first time by Fujii and Ohba 146) from the (-)-ethyl ester of 103 through the debenzylated ester 73 (R = C02Et). Wolff-Kishner reduction of 73 (R = CHO) produced the (-)-2-ethyl congener 73 (R = Me) 146). 

Both the Clemmensen and the Wolff-Kishner reductions are designed to carry out a specific functional group transformation the reduction of an aldehyde or ketone carbonyl to a methylene group Neither one will reduce the carbonyl group of a carboxylic acid nor... 

Table 17 2 summarizes the reactions of aldehydes and ketones that you ve seen m ear her chapters All are valuable tools to the synthetic chemist Carbonyl groups provide access to hydrocarbons by Clemmensen or Wolff-Kishner reduction (Section 12 8) to alcohols by reduction (Section 15 2) or by reaction with Grignard or organolithmm reagents (Sections 14 6 and 14 7)... 

Wolff-Kishner reduction (Section 12 8) Method for reducing the carbonyl group of aldehydes and ketones to a methylene... 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Another important synthetic method for the reduction of ketones and aldehydes to the corresponding methylene compounds is the Woljf-Kishner reduction. This reaction is carried out under basic conditions, and therefore can be applied for the reduction of acid-sensitive substrates it can thus be regarded as a complementary method. The experimental procedure for the Clemmensen reduction is simpler however for starting materials of high molecular weight the Wolff-Kishner reduction is more successful. 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C—has been replaced almost completely by the modified procedure after Huang-Minlon The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tcrt-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

The deoxygenation of aldehydes and ketones to the corresponding hydrocarbons via the hydrazones is known as the Wolff-Kishner reduction.28 Various modifications of the original protocols have been suggested. One of the most useful is the Huang-Minlon modification, which substituted hydrazine hydrate as a safer and less expensive replacement of anhydrous hydrazine. In addition, diethylene glycol together with sodium hydroxide was used to increase the reaction... 

This silyl hydrazone formation-oxidation sequence was originally developed as a practical alternative to the synthesis and oxidation of unsubstituted hydrazones by Myers and Furrow [31]. The formation of hydrazones directly from hydrazine and ketones is invariably complicated by azine formation. In contrast, silyl hydrazones can be formed cleanly from /V,/V -bis(7< rt-butyldimethylsilyl)hydrazine and aldehydes and ketones with nearly complete exclusion of azine formation. The resulting silylhydrazones undergo many of the reactions of conventional hydrazones (Wolff-Kishner reduction, oxidation to diazo intermediate, formation of geminal and vinyl iodides) with equal or greater efficiency. It is also noteworthy that application of hydrazine in this setting may also have led to cleavage of the acetate substituents. 

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