Ketones from aliphatic nitro compounds

Reaction of carbanions with TNB may result in the formation of new carbon-carbon bonds. Examples of adducts formed are (63) from ketones [166], (64) from aliphatic nitro compounds [167], and (65) from malononitrile [168]. ThCTe are various possibilities for furtho- reaction of these adducts. These include the formation of diadducts or of uicia-bridged adducts, such as (66), from suitable ketones [169,170] or from amidines, or of the ionization of the exocyclic hydrogen in (65) to give a dianion. 

Removal of a proton from an aliphatic nitro compound gives a carbanion (R2C —NO2) that can be alkylated at oxygen or carbon. 0-Alkylation gives nitronic esters, which are generally unstable to heat but break down to give an oxime and an aldehyde or ketone. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The most conspicuous property of aliphatic amines, apart from their fishy smell, is their high basicity, which usually precludes N-alkylations under acidic reaction conditions (last reaction, Scheme 6.3). Hence, alkylation of amines with tertiary alkyl groups is not usually possible without the use of highly stabilized carbocations which can be formed under basic reaction conditions. Rare exceptions are N-alkyla-tions of amines via radicals (Scheme 4.2), copper-catalyzed propargylations (Scheme 6.3), and the addition of amines to some Michael acceptors and allyl palladium or iridium complexes. Better strategies for the preparation of tert-alkylamines include the addition of Grignard reagents to ketone-derived imines [13] or the reduction of tert-alkyl nitro compounds. 

Dioxiranes, prepared from acetone and other aliphatic ketones by treatment with Oxone, can accomplish oxidations that are usually not achieved by Oxone itself [210, 211], Dioxiranes can be isolated by vacuum codistillation with the respective ketones [210], or else, they may be formed in situ and applied in the same reaction vessel [210, 211]. Examples of the applications of dioxiranes are epoxidations 210] and the oxidation of primary amines to nitro compounds [211], of tertiary amines to amine oxides [210], and of sulfides to sulfoxides [210] (equation 12). 

The higher rate of O-protonation than that of C-protonation at temperatures when the thermodynamic stability of the oxonium cation is lower than or comparable with that of the C-protonated form has analogies. Thus, mesomeric anions formed by the heterolysis of a-C—H bonds of aliphatic ketones and nitro compounds are usually more readily protonated at O than at C though a thermodynamically less stable tautomer (enol, an acinitro form) is formed. TTiese deviations from the Bronsted principle are explained 34i. 342> O-protonation requiring a smaller rearrangement... 

Lower valent tungsten halides are a new class of deoxygenation agents, e.g. for the conversion of carbonyl or epoxy compounds into olefins . A new reagent, generated in situ from iron pentacarbonyl and a small amount of base in moist solvents, selectively and efficiently hydrogenates the ethylenic portion of a,/ -unsaturated carbonyl compounds, such as ketones or lactones, under mild conditions. Aliphatic tert. amides can be easily reduced to alcohols by alkali metals in hexa-methylphosphoramide and a protic cosolvent such as tert-butanol. Aldehydes can be obtained from acids by catalytic reduction of intermediate carboxylic alkoxyformic anhydrides . Sec. nitro compds. are converted into ketones by the joint action of a nitrite ester and NaNOg under mild, non-acidic conditions . 

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