Nitro stability

Cyclization of nitro-stabilized radicals provides another method for the generation of cyclic nitronates (221). Oxidation of the aci-foim of nitroalkanes with ceric ammonium nitrate generates the ot-carbon centered radical, which in the presence of an alkene, leads to the homologation of the a-radical. In the case of a tethered alkene of appropriate length, radical addition leads to a cyclic nitronate (Scheme 2.20). 

The nitro group is one of the best activating groups for conjugate addition as it almost never gives direct addition. Even the weakly nucleophilic acetate ion will react as the nitro-stabilized anion is very stable indeed. 

In conclusion, C-C bond formation on carbohydrates has absorbed lots of widely used methods from general synthetic organic chemistry. Typical among these methods are intramolecular alkylation and intramolecular condensation of aldehyde with enolates, phosphonates, and nitro-stabilized anions. Metal-mediated radical reactions, cycloadditions, and rearrangements have also been applied frequently. 

Nitro-stabilized anions also undergo additions to aldehydes, ketones, and electrophilic alkenes these reactions appear in Chapters 27 and 29. 

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. 

In recent work Kende and his coworkers have explored intramolecular oxidative coupling between phenolate and enolate, rather than between two phenolates. This proved a viable process for certain carbonyl enolates, and for nitro-stabilized anions, llius potassium ferricyanide oxidations of the indandione... 

The utilization of carbanions stabilized by various electron-withdrawing groups to effect carbon-carbon bond formation occupies a central position in organic synthesis. This chapter focuses on the reactions of nitro-stabilized carbanions (nitronate anions or their equivalents) with aldehydes and ketones. This route for the coupling of a carbonyl and a nitroalkane component, leading to vicinal nitro alcohols, was discovered in 1895 by Henry and is currently known as the Henry or nitroaldol reaction. 

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