Conjugated oximes, reductive conversion

Reductive conversion of allylic nitro compounds into conjugated oximes... 

On the other hand, conjugated nitroalkenes are very useful electron-poor alkenes, prone to act as nucleophilic acceptor, mainly in the Michael reaction (Berestovitaskaya et al., 1994) or in the Diels-Alder cycloaddition (Denmark and Thorarensen, 1996). Moreover, the nitro group can be easily turned into a respectable array of functional groups such as its reduction to a primary amine, replacement with hydrogen (Ballini et al., 1983 Ono, 2001), conversion into a carbonyl (Nef reaction) (Ballini and Petrini, 2004), and transformation into other important functionalities such as nitrile, nitrile oxide, oximes, hydroxylamines, and thiols (Colvin et al., 1979). 

OXIMES AND SEMICARBAZONES Ceric ammonium nitrate. CLEMMENSEN REDUCTION Zinc dust. COMPLEX OF BENZYNE. Nickel carbonyl. n-COMPLEXES Diiron nonacarbonyl. CONDENSING AGENT Calcium carbide. CONJUGATE ADDITION Dimethylcop-perlithium. Nickel carbonyl. Tetrakisjiodo-(tri-ff-butylphosphine)copper(I)]. CONVERSION OF PHENOLS TO ARYL BROMIDES Triphenylphosphine dibromide. 

Conversion of ketoximes into ketones. Corey and Richman1 have reported a new procedure for regeneration of ketones from their oximes. The oxime is first converted into the O-acetate by treatment with acetic anhydride at 20° this derivative is then reductively deoximated by treatment with > 2 molar equivalents of chromous acetate in 9 1 THF-water at 25-65°. The reaction presumably involves reductive fission of the oxime N—O linkage to give an imine which is then rapidly hydrolyzed. Yields are in the range 75-85%. It is noteworthy that the reaction occurs more readily with acetoximes of conjugated ketones than with those of nonconjugated ketones and that the reaction occurs readily with acetoximes of hindered ketones such as camphor. 

The reduction of ketoximes with titanium(iu) chloride is noted in a partial synthesis of erythromycylamine in this case, the intermediate imine is stable and can be further reduced, though normally imine hydrolysis is rapid and ketones are obtained in high yield. This observation has been utilized to effect conversion of a nitro-compound into a ketone. In search of a route to 1,4-diketones via conjugate addition of a masked carbonyl anion to an ajS-unsaturated ketone, McMurry considered Michael addition with a nitro-alkane. Treatment of the resulting y-nitroketone with titanium(m) chloride afforded the required 1,4-diketone (148) in excellent yield, presumably by sequential intermediacy of the oxime and the imine this mild conversion avoids the harsh conditions of the alternative Nef procedure (Scheme 69). 

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