Nitro enolate

Xenon difluoride reaction with nitro enolates provides a useful entry into a wide variety of fluonnated synthetic intermediates [91 92] (equation 52)... 

One of these involves ozonolysis of the nitro enolate at low temperature rather than treatment with n... 

THF reduces aliphatic nitro enolate anions to hydroxylamines ... 

The nitro group can be converted into other useful functional groups following conjugate addition. Reduction gives primary amines while hydrolysis reveals ketones. The hydrolysis is known as the Nef reaction and used to be achieved by formation of the nitro-stabilized anion with a base such as sodium hydroxide followed by hydrolysis with sulfuric acid. These conditions are rather unforgiving for many substrates (and products) so milder methods have been developed. One of these involves ozonolysis of the nitro enolate at low temperature rather than treatment with acid. 

Note that nitro enolates have other synthetic uses. When nitrobutane was treated with sodium hydroxide, nitro-enolate 205 was formed. Rather than addition of an aldehyde or a ketone, 205 was treated with concentrated sulfuric acid to form butanal, with loss of N2O, in what is known as the Nef reaction. 28 Modern versions of this reaction use bases such as LDA and less vigorous oxidizing agents such as MoOPh. 29 The Knoevenagel disconnection is ... 

Acid catalysis is preferable to base for the condensation of 5a-cholestan-3-one (341) with pentyl nitrite to form the hydroxyimino-ketone (342). The dioxime (343) afforded the [2,3-c]furazan 2-oxide (344) on oxidation with hypochlorite. Nitration of the 3-ketone (341) with ethyl nitrate and base gave the 2-nitro-enol (345) the derived 3-oxime (346) gave the furazan oxide (344) on reaction with acid. Nitration of 5a-cholestan-7-one gave the 6a- and 6)5-nitro-ketones (347), apparently the first epimeric pair of steroidal nitro-ketones to be... 

Excited states of ketones (compound I) and positive solvatochromic dyes, e.g. diethylamino p-nitrobenzene (compound II of table VII) or related compounds are more strongly solvated by polar solvents when comparki with apolar ones. The shift of the K a transition of substituted p-nitro enoles as well as the n a transition of ketones are used as empirical polarity scales, a and % of a solvent. The energy shifts of the a a transition of substituted pyridinium-N-phenoIate betaines (compound III) and the charge-transfer absorption... 

Reaction of ethyl crotonate and nitroethane in the presence of the basic 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU) led to nitro-ester 3.49 in 74% yield.31 Catalytic hydrogenation of the nitro group and acid hydrolysis produced 3-methyl-4-amino-butanoic acid, 3.50. Choosing different conjugated esters as starting materials led to formation of 3-ethyl- (59% overall yield) 3-propyl- (51% overall yield) 3-isopropyl-(62% overall yield) 3-butyl- (56% overall yield) 3-sec-butyl- (60% overall yield) 3-isobutyl- (58% overall yield) and, 3-r-butyl-4-aminobutanoic acid (31% overall yield).31 The yields observed in this study clearly show that conjugate addition of nitro enolates is a synthetically useful process. 

An example of this process is the reaction of nitromethane with sodium meth-oxide to give the nitro enolate. Subsequent reaction with methyl 3-bromopropanoate gave a nitro-ester, and catalytic hydrogenation led to 4-aminopentanoic acid (4.105) in 19% overall yield. O The enolate of nitroethane reacted similarly with methyl... 

Another related method uses the anion of nitroalkanes in a reaction with halo-esters. Nitromethane reacted with lithium diisopropylamide to form the nitro enolate and then with methyl 3-chloropentanoatc to give 4.110. Reduction of the nitro group with ammonium formate gave methyl 2-phenyl-3-aminopropanoate, 4.111. 

In a very different condensation reaction, nitro enolates derived from nitro acetates reacted with orthoesters, in the presence of an amine, to give aminopro-penoic acid derivatives. Ethyl a-nitroacetate, for example, was converted to ethyl 3-(N-phenylamino)-2-nitroprop-2-enoate, 4.115, in good yield. 

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