Wolff-Kishner reduction, of aldehydes and ketones

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... 

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... 

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... 

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). 

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... 

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

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. 

Dithioacetals of aldehydes and ketones are transformed to the corresponding methylene compounds by treatment with Raney Ni. This transformation may be used in place of the methods known as Clemmensen or Wolff-Kishner reduction. The method using Raney Ni is advantageous in that the reaction can be performed under a neutral condition. Typical examples are given in eqs. 13.84,131 13.85,163 and 13.86.164 In the example in eq. 13.86, desulfurization afforded a high yield of 4-cholestene without affecting the A4 double bond. 

Three common procedures are available for the transformation of aldehydes and ketones to hydrocarbons (1) reduction by zinc and hydrochloric acid (Clemmensen), (2) reduction by hydrazine in the presence of a base (Wolff-Kishner), and (3) catalytic hydrogenation. In view of the complicated mixtures obtained by the polyalkylation of benzene by the Friedel-Crafts reaction (method 1), reduction of alkyl aryl ketones is the most reliable method for the preparation of di- and poly-alkylbenzenes. 

Direct transition from level 2 to level 0 can be achieved by way of the Wolff-Kishner reaction (treatment of the respective hydrazones with alkali), a classical pathway for the reduction of carbonyl compounds. At the same time, a direct conversion of aldehydes and ketones into alkenes is also feasible via reductive cleavage of their tosylhydrazones under the action of MeLi, the Shapiro reaction (Scheme 2.63). "... 

Since its introduction early in this century, the deoxygenation of aldehydes and ketones to methyl or methylene derivatives, respectively, via base treatment of hydrazone intermediates (equation 1) has proven to be one of the most convenient and synthetically useful processes available for this important type of transformation. The reaction is termed the Wolff-Kishner reduction in recognition of the two original independent discoverers.However, the initial recipes introduced proved tedious and unreliable with many structural, especially hindered, examples. This led to substantial efforts devoted over the years to developing more convenient and successful experimental procedures, resulting in a number of improved and more reliable modifications which are most often utilized at present. More recently, modified procedures have been provided which utilize hydride reductions of p-toluenesulfonylhydrazone (to-sylhydrazone) derivatives and subsequent decomposition to release the hydrocarbon products under much milder and less basic conditions than those normally required for Wolff-Kishner reductions (equation 2). 

Deoxygenation of the carbonyl group of aldehydes and ketones via the intermediacy of their hydrazone derivatives, known as the Wolff-Kishner reduction,offers an alternative to the thioacetal desulfurization method. The Wolff-Kishner reduction in the presence of hydrazine and NaOH (or KOH) has been replaced largely by the Huang-Minlon method,where the deoxygenation is carried out with hydrazine in refluxing ethylene glycol. 

Wolff-Kishner reduction Deoxygenation of aldehydes and ketones under basic conditions to give hydrocarbons via the corresponding hydrazones or semicarbazones. 496... 

Under ordinary conditions, carbonyl groups of aldehydes and ketones will not be reduced by catalytic hydrogenation, but if Raney nickel (Ni-ff2) is used as the catalyst, then a reduction takes place giving an alcohol product. If the ketone or aldehyde is first converted to a dithiane, then Raney nickel reduction will give an alkane product (see Clemmenson and Wolff-Kishner reductions below as alternatives for this same transformation). 

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... 

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