From unsaturated nitro compounds

The enantiomeric reduction of 2-nitro-l-phenylprop-l-ene has been studied in a range of Gram-positive organisms including strains of Rhodococcus rhodochrous (Sakai et al. 1985). The enantiomeric purity of the product depended on the strain used, the length of cultivation, and the maintenance of a low pH that is consistent with the later results of Meah and Massey (2000). It has been shown that an NADPH-linked reduction of a,p-unsaturated nitro compounds may also be accomplished by old yellow enzyme via the flcf-nitro form (Meah and Massey 2000). This is formally analogous to the reduction and dismutation of cyclic enones by the same enzyme (Vaz et al. 1995), and the reductive fission of nitrate esters by an enzyme homologous to the old yellow enzyme from Saccharomyces cerevisiae (Snape et al. 1997). 

The addition-elimination reaction of hetero-atom-substituted nitroalkenes provides functionalized derivatives of unsaturated nitro compounds.26 Nitroenamines are generally prepared from a-nitro ketones and amines (see Chapter 5 regarding acylation of nitro compounds).26... 

When the stereogenic center is situated at the allylic position, as in nitroethyl ethers derived from 5,6-unsaturated nitro compounds, only the endo-isomer (trans) of the bicyclic structure was formed (Scheme 6.45) (256). 

Although the reduction of nitro compounds is more widely applied in the aromatic series using procedures discussed in Section 6.5.1, p. 890, these are equally applicable to the reduction of primary or secondary nitroalkanes when these are readily available. a,/ -Unsaturated nitro compounds (arising for example from the Claisen-Schmidt reaction, Section 6.12.2, p. 1032) may be reduced to the saturated amine very effectively with sodium dihydrobis(2-methoxyethoxy)-aluminate ( Red-Al ). 

Other groups beside nitro can be reduced in the same step. So the diamine 19, needed for polyamine manufacture, could come from the unsaturated nitro compound 20 that would in turn come from an aldol reaction between the anion of nitromethane 1 and the aldehyde 21. This has a 1,5-diX relationship and acrylonitrile 23 is excellent at conjugate addition (chapter 21) so we can use isobutyraldehyde 24 as a starting material. 

As illustrations of the variety of methods available, the three processes below show (i) the addition of isonitrile anions to a,P-unsaturated nitro-compounds, with loss of nitrous acid to bring about aromatisation, (ii) the interaction of thioglycolates with 1,3-dicarbonyl-compounds, for the synthesis of thiophene 2-esters, and (iii) the cycloaddition/cycloreversion preparation of furans from oxazoles. 

From Tosylmethyl Isocyanide and oc,P-Unsaturated Esters or Ketones and from Isocyano-Acetates and a,P-Unsaturated Nitro-Compounds... 

In tMs approach, conjugate addition of the anion from an isocyano-acetate to an a,p-unsaturated nitrocompound with evenmal loss of nitrous acid, produces 5-unsubstituted pyrrole-2-esters. The example below shows a mechanistic sequence that can be seen to parallel that in the van Leusen synthesis. The most useful route to the a,P-unsaturated nitro-compound involves the base-catalysed condensation of an aldehyde with a nitroalkane giving an a-hydroxy-nitroalkane it can alternatively be generated in situ, in the presence of the isonitrile, using diazabicycloundecane (DBU) as base on the 0-acetate of the a-hydroxy-nitroalkane (for an example see 16.16.2.1). The process works even when the unsaturated nitro unit is a component of a polycyclic aromatic compound. ... 

From tosylmethylisocyanide and a,/3-unsaturated esters or ketones and from isocyano acetates and a,(5-unsaturated nitro compounds... 

Ranitidine s right-hand portion is made in a simiiar way from an unsaturated nitro compound. This time the methyi-amine substitution is done first, foiiowed by addition of the rest of the moiecuie. 

A study of the thermal reactions of the unsaturated nitro-compounds (67) and (68) ((nrepared from the ketone CFs CO-CFa NOs) has shown that intramolecular condensation of the nitro-group with the double bonds (fi-y and y-S, respectively) does not take place (see Scheme 44). ... 

A nitroalkane with a chiral centre on the beta-carbon, which is generated by Michael reaction of a thiol to an a,p-unsaturated nitro compound, racem-izes under reversible Michael conditions and may be applied for DKR [108]. The racemic Michael adduct from ethyl 3-(2-mercaptophenyl)-2-propenoate and P-nitrostyrene is racemized in thepresence of thiourea and cychzes by a second Michael reaction of the carbon alpha to the nitro group to the a,p-unsaturated ester to give thiochromene, which has three consecutive stereogenic centres, in 95% yield with 95% ee as almost a single diastereomer (Scheme 5.35) [108aj. 

The two major methods of preparation are the cycloaddition of nitrile oxides to alkenes and the reaction of a,/3-unsaturated ketones with hydroxylamines. Additional methods include reaction of /3-haloketones and hydroxylamine, the reaction of ylides with nitrile oxides by activation of alkyl nitro compounds from isoxazoline AT-oxides (methoxides, etc.) and miscellaneous syntheses (62HC(i7)i). 

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