Conjugate addition nitro-alkanes

Rann et al. reported the dramatic influence of a new tailor-made, task-specific, and stable ionic liquid, butyl methyl imidazolium hydroxide ([bmim][OH]), in Michael addition. They have discovered that a task-specific ionic liqnid [bmim][OH] efficiently promoted the Michael addition of 1,3-dicarbonyl compounds, cyano esters, and nitro alkanes to a variety of conjugated ketones, carboxylic esters, and nitriles withont reqniring any other catalyst and solvent (Fig. 12.21) [16]. Very interestingly, all open-chain 1,3-dicarbonyl componnds such as acetylacetone, ethyl ace-toacetate, diethyl malonate, and ethyl cyanoacetate reacted with methyl vinyl ketone and chalcone to give the usual monoaddition products, whereas the same reactions with methyl acrylate or acrylonitrile provided exclusively bis-addition products. 

Nitro groups can assist in the introduction of alkyl groups into esters in two ways, either by conjugate addition of a nitro-alkane to an acrylate [(77) (78)] or by the addition of... 

Scheme 15.25 As5mimetric conjugated addition of alkyl zinc reagents to nitro-alkanes emplo5dng a chiral copper catalyst.

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). 

Short peptides have been used both to catalyze the conjugate addition of nitro-alkanes to a,(i-unsaturated ketones, and the addition of enolates of aldehydes to nitroolefins. 

The derivatives 3 and 6 without any additional modification at the C9 position are infrequently used for organocatalysis. Recent examples include the synthesis of enantioenriched 1,3,4-trisubstituted thiochromanes by a tandem conjugate addition-Henry reaction between 2-thio-substituted benzaldehydes and nitrosty-renes (Scheme 6.10) [26] and the Henry reaction between isatin and simple nitro-alkanes to form 3-substituted 3-hydro-oxindoles (Scheme 6.11) [27]. 

Zhu Q, Lu YX. Enantioselective conjugate addition of nitro-alkanes to vinyl sulfone an organocatalytic access to chiral amines. Org. Lett. 2009 11(8) 1721-1724. 

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