3-Nitro-2-cyclohexenone

DIENOPH1LES Acrolein. Ethynylp-tolyl sulfonc. 3-Mcthylsulfony 1-2,5-dihydro-furane. 3-Nitro-2-cyclohexenone. Phenyl vinyl sulfone. 

Ethanol, 2-nitro-, 41, 67 conversion to nitroethylene, 41, 71 Ether, tert-butyl phenyl, 41, 91 Etherification of cholestanol, 41, 9 with diazomethane, 41, 9 3-Ethoxy-2-cyclohexenone, 40, 41 reduction to 2-cyclohexenone, 40, 14... 

The acidifying effect of the nitro group is so profound that very mild bases can be used to catalyse the reaction. This enables selective removal of the proton next to the nitro group and helps to avoid side-reactions involving aldol condensations of the carbonyl component, Common examples include amines, quaternary ammonium hydroxides, and fluorides, Even basic alumina is sufficient to catalyse virtually quantitative addition of this benzylic nitroalkane to cyclohexenone at room temperature ... 

The Hill synthesis 104) of 4-nitro-2,6-diphenylphenol from nitro-malonaldehyde and dibenzylketone was the first example of a useful synthesis by which many similar 2,6-diaryl-substituted cyclohexenone- and 2,6-diarylphenol derivatives have since been prepared. 

The nitro alkenes are useful for further transformations, 12 of which were reported in the case of 2. Thus 2 is converted into cyclohexenone in 70% yield by... 

Diels-Alder reactions. This reagent is more reactive in Diels-Alder reactions than cyclohexenone. Treatment of the /i-nitro ketone with DBN effects elimination of HNO, to form the a,/ -enone.2 Thus the final products correspond to adducts of a cyclohexynone, but with reversed regioselectivity. 3-Nitro-2-cyclopentenone, m.p. 69-71°, is also a useful dienophile (second example). 

Only activated monoenes are hydrogenated . These include carvene, mesityl oxide, 2-cyclohexenone, and benzalacetone . Some styrenes are hydrogenated a-functionalized styrenes react, but )S-functionalized styrenes do not - " . Similarly, only activated ketones such as benzil, diacetyl and p-benzoquinone are hydrogenated to alcohols " . Often catalytic reduction of a ketone is observed only in the presence of added OH . The base is believed to react with an intermediate to give [Co(CN)j(OH)] and the reduced substrate . Aryl ketones such as acetophenone and benzophenone are not reduced . Several examples of nitro and nitroso compound reductions have been reported - . ... 

A new catalyst incorporating chiral thiourea and nucleophilic Lewis base showed efficiency in the asymmetric BH reactions. The use of a binaphthyl-based amino-thiourea catalyst 63 synthesized by Wang et al. [ 114] resulted in good yields and enantioselectivities in the reaction of cyclohexenone and aldehydes. Another amino-thiourea 12 was demonstrated as an efficient bifunctional catalyst for the enantio-selective aza-BH reaction of (3-methyl-nitrostyrene and iV-tosyl-aldimines, affording P-nitro-y-enamines in modest to excellent enantioselectivities and diastereoselec-tivities (Scheme 9.32). It was found that no reaction occurred in the absence of the methyl group of nitroalkene [115]. A similar phophine-thiourea catalyst 64 was reported in 2008 by Wu and co-workers [116] and turned out to be efficient in the asymmetric BH reaction of MVK and aldehydes, providing fast reaction rate, good yields, and excellent enantioselectivities (87-94% ee). More recently, aL-threonine-derived phosphine-thiourea catalyst 65 was readily synthesized by Lu and coworkers [117] and applied in the enantioselective BH reaction of aryl aldehyde with methyl acrylate. 

Reaction of 1-N-pyrrolidinocyclohexene with -nitroacetophenone or ethyl -nitrobenzoate results in reduction of the nitro group to amino and formation of 2-N-pyrrolidinocyclohex-2-en-l-one67 Reduction of nitrobenzene to aniline is sluggish the enamine is converted to o-pyrrolidinophenol, not to a cyclohexenone. Literature procedures for preparation of enamines via titanium-amine complexes, Ti(NR2)4, often hampered by the somewhat tedious methods available for preparation of the titanium reagent. An improved enamine synthesis utilizes a stoichio-... 

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